patch(1): don't assume a match if we run out of context to check

Patches with very little context (-U0 and -U1) could get misapplied if
the file to be patched changes and a hunk is no longer applicable. Matching
with fuzz would be attempted and default to a match when we unexpectedly ran
out of context.

PR:		74127
Reviewed by:	emaste, pfg
Approved by:	emaste (mentor)
Differential Revision:	https://reviews.freebsd.org/D12631

usr.bin/patch/patch.c

@@ -1026,6 +1026,9 @@ patch_match(LINENUM base, LINENUM offset, LINENUM fuzz)
 	const char	*plineptr;
 	unsigned short	plinelen;
 
+	/* Patch does not match if we don't have anymore context to use */
+	if (pline > pat_lines)
+		return false;
 	for (iline = base + offset + fuzz; pline <= pat_lines; pline++, iline++) {
 		ilineptr = ifetch(iline, offset >= 0);
 		if (ilineptr == NULL)