Fix segmentations failure in error.c gumbo_caret_diagnostic_to_string#1

c1n1c merged 1 commit intoabak-press:masterabak-press/gumbo-parser:masterfrom

DmitryBochkarev:segmentation_failure_fixDmitryBochkarev/gumbo-parser:segmentation_failure_fixCopy head branch name to clipboard