More cautious legacy_color conversion in Logging (JuliaLang#53280)

Can be seen as a follow-on from JuliaLang#51829, also wants
JuliaLang/StyledStrings.jl#37
 to behave as expected.

Author: tecosaur

stdlib/Logging/src/ConsoleLogger.jl

@@ -148,7 +148,10 @@ function handle_message(logger::ConsoleLogger, level::LogLevel, message, _module
     # Format lines as text with appropriate indentation and with a box
     # decoration on the left.
     color, prefix, suffix = logger.meta_formatter(level, _module, group, id, filepath, line)::Tuple{Union{Symbol,Int},String,String}
-    color = StyledStrings.Face(foreground=StyledStrings.Legacy.legacy_color(color))
+    lcolor = StyledStrings.Legacy.legacy_color(color)
+    if !isnothing(lcolor)
+        color = StyledStrings.Face(foreground=lcolor)
+    end
     minsuffixpad = 2
     buf = IOBuffer()
     iob = IOContext(buf, stream)