ignore mapping if line is not set (#208)

Author: esskar

lib/getMapping.js

@@ -8,11 +8,11 @@ const { SourceMapConsumer } = require('source-map');
  */
 module.exports = function getMapping(sourceMap, location) {
 	/* istanbul ignore if: edge case too hard to test for with babel malformation */
-	if (location.start.line < 1 || location.start.column < 0) {
+	if (!location.start.line || location.start.line < 1 || location.start.column < 0) {
 		return null;
 	}
 	/* istanbul ignore if: edge case too hard to test for with babel malformation */
-	if (location.end.line < 1 || location.end.column < 0) {
+	if (!location.end.line || location.end.line < 1 || location.end.column < 0) {
 		return null;
 	}