Fix sanitizer warning (#771)

* Let's try this

* Fix out-of-bounds access in MULRK struct handling

* Take 2

In response to seeing this:

libxls/xls.c:589:23: runtime error: load of misaligned address 0x50700005cbb6 for type 'DWORD', which requires 4 byte alignment

* Move and turn into inline functions

The use of inline functions is in response to this:

Found the following significant warnings:
  libxls/xls.c:121:31: warning: ISO C forbids braced-groups within expressions [-Wpedantic]
  libxls/xls.c:126:34: warning: ISO C forbids braced-groups within expressions [-Wpedantic]

* Apply fix to another MULRK location

* Revert "Apply fix to another MULRK location"

This reverts commit 738df8a.

* Craft a similar fix for MULBLANK (not MULRK, oops)

* Fix for access inside LABEL

* Adopt patch strategy used in positron

* Revert whitespace changes I did not mean to make earlier

* Moar checks

* Get rid of trailing comma

.github/workflows/rhub.yaml

@@ -27,7 +27,7 @@ on:
       config:
         description: 'A comma separated list of R-hub platforms to use. These default choices have been customized for readxl.'
         type: string
-        default: 'gcc-asan,valgrind,rchk,gcc15'
+        default: 'gcc-asan,valgrind,rchk,gcc15,clang-asan,clang-ubsan'
       name:
         description: 'Run name. You can leave this empty now.'
         type: string

src/libxls/xls.c

@@ -478,7 +478,10 @@ int xls_isCellTooSmall(xlsWorkBook* pWB, BOF* bof, BYTE* buf) {
         if (bof->size < offsetof(LABEL, value) + 2)
             return 1;
 
-        size_t label_len = ((LABEL*)buf)->value[0] + (((LABEL*)buf)->value[1] << 8);
+        // --- Start readxl ---
+        BYTE *value = get_LABEL_value((LABEL*)buf);
+        size_t label_len = value[0] + (value[1] << 8);
+        // --- End readxl ---
         if (pWB->is5ver) {
             return (bof->size < offsetof(LABEL, value) + 2 + label_len);
         }
@@ -580,8 +583,10 @@ static struct st_cell_data *xls_addCell(xlsWorkSheet* pWS,BOF* bof,BYTE* buf)
             }
             cell=&row->cells.cell[index];
             cell->id=XLS_RECORD_RK;
-            cell->xf=xlsShortVal(((MULRK*)buf)->rk[i].xf);
-            cell->d=NumFromRk(xlsIntVal(((MULRK*)buf)->rk[i].value));
+            // --- Start readxl ---
+            cell->xf=xlsShortVal(get_MULRK_RK_XF((MULRK*)buf, i));
+            cell->d=NumFromRk(xlsIntVal(get_MULRK_RK_VALUE((MULRK*)buf, i)));
+            // --- End readxl ---
             xls_cell_set_str(cell, xls_getfcell(pWS->workbook,cell, NULL));
         }
         break;
@@ -595,7 +600,9 @@ static struct st_cell_data *xls_addCell(xlsWorkSheet* pWS,BOF* bof,BYTE* buf)
             }
             cell=&row->cells.cell[index];
             cell->id=XLS_RECORD_BLANK;
-            cell->xf=xlsShortVal(((MULBLANK*)buf)->xf[i]);
+            // --- Start readxl ---
+            cell->xf=xlsShortVal(get_MULBLANK_XF((MULBLANK*)buf, i));
+            // --- End readxl ---
             xls_cell_set_str(cell, xls_getfcell(pWS->workbook,cell, NULL));
         }
         break;

src/libxls/xlsstruct.h

@@ -37,6 +37,9 @@
 #define XLS_STRUCT_INC
 
 #include "libxls/ole.h"
+// --- Start readxl ---
+#include <string.h>
+// --- End readxl ---
 
 #define XLS_RECORD_EOF          0x000A
 #define XLS_RECORD_DEFINEDNAME  0x0018
@@ -204,6 +207,19 @@ typedef struct MULRK
 }
 MULRK;
 
+// --- Start readxl ---
+static inline WORD get_MULRK_RK_XF(MULRK *mulrk, int i) {
+    WORD xf;
+    memcpy(&xf, (BYTE *)mulrk + offsetof(MULRK, rk) + i * (sizeof(WORD) + sizeof(DWORD)), sizeof(WORD));
+    return xf;
+}
+
+static inline DWORD get_MULRK_RK_VALUE(MULRK *mulrk, int i) {
+    DWORD value;
+    memcpy(&value, (BYTE *)mulrk + offsetof(MULRK, rk) + i * (sizeof(WORD) + sizeof(DWORD)) + sizeof(WORD), sizeof(DWORD));
+    return value;
+}
+// --- End readxl ---
 typedef struct MULBLANK
 {
     WORD	row;
@@ -213,6 +229,14 @@ typedef struct MULBLANK
 }
 MULBLANK;
 
+// --- Start readxl ---
+static inline WORD get_MULBLANK_XF(MULBLANK *mulblank, int i) {
+    WORD xf;
+    memcpy(&xf, (BYTE *)mulblank + offsetof(MULBLANK, xf) + i * sizeof(WORD), sizeof(WORD));
+    return xf;
+}
+// --- End readxl ---
+
 typedef struct BLANK
 {
     WORD	row;
@@ -230,6 +254,12 @@ typedef struct LABEL
 }
 LABEL;
 
+// --- Start readxl ---
+static inline BYTE *get_LABEL_value(LABEL *label) {
+    return (BYTE *)label + offsetof(LABEL, value);
+}
+// --- End readxl ---
+
 typedef struct BOOLERR
 {
     WORD    row;