[PATCH] Re-Fix SIGSEGV on unmerged files in git-diff-files -p

When an unmerged path was fed via diff_unmerged() into diffcore,
it eventually called run_diff() with "one" and "two" parameters
with NULL, but run_diff() was not written carefully enough to
notice this situation.
Signed-off-by: NJunio C Hamano <junkio@cox.net>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

diff.c

@@ -555,6 +555,7 @@ static void run_diff(const char *name,
 {
 	const char *pgm = external_diff();
 	if (!pgm &&
+	    one && two &&
 	    DIFF_FILE_VALID(one) && DIFF_FILE_VALID(two) &&
 	    (S_IFMT & one->mode) != (S_IFMT & two->mode)) {
 		/* a filepair that changes between file and symlink

diffcore.h

@@ -33,7 +33,7 @@ struct diff_filespec {
 				  * if false, use the name and read from
 				  * the filesystem.
 				  */
-#define DIFF_FILE_VALID(spec) ((spec) && ((spec)->mode) != 0)
+#define DIFF_FILE_VALID(spec) (((spec)->mode) != 0)
 	unsigned should_free : 1; /* data should be free()'ed */
 	unsigned should_munmap : 1; /* data should be munmap()'ed */
 };