merge-file: refactor for subsequent memory leak fix

Refactor the code in builtin/merge-file.c to:

 * Use the initializer to zero out "mmfs", and use modern C syntax for
   the rest.

 * Refactor the the inner loop to use a variable and "if/else if"
   pattern followed by "return". This will make a change to change it to
   a "goto cleanup" pattern smaller.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

builtin/merge-file.c

@@ -25,10 +25,10 @@ static int label_cb(const struct option *opt, const char *arg, int unset)
 
 int cmd_merge_file(int argc, const char **argv, const char *prefix)
 {
-	const char *names[3] = { NULL, NULL, NULL };
-	mmfile_t mmfs[3];
-	mmbuffer_t result = {NULL, 0};
-	xmparam_t xmp = {{0}};
+	const char *names[3] = { 0 };
+	mmfile_t mmfs[3] = { 0 };
+	mmbuffer_t result = { 0 };
+	xmparam_t xmp = { 0 };
 	int ret = 0, i = 0, to_stdout = 0;
 	int quiet = 0;
 	struct option options[] = {
@@ -71,21 +71,23 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 
 	for (i = 0; i < 3; i++) {
 		char *fname;
-		int ret;
+		mmfile_t *mmf = mmfs + i;
 
 		if (!names[i])
 			names[i] = argv[i];
 
 		fname = prefix_filename(prefix, argv[i]);
-		ret = read_mmfile(mmfs + i, fname);
+
+		if (read_mmfile(mmf, fname))
+			ret = -1;
+		else if (mmf->size > MAX_XDIFF_SIZE ||
+			 buffer_is_binary(mmf->ptr, mmf->size))
+			ret = error("Cannot merge binary files: %s",
+				    argv[i]);
+
 		free(fname);
 		if (ret)
-			return -1;
-
-		if (mmfs[i].size > MAX_XDIFF_SIZE ||
-		    buffer_is_binary(mmfs[i].ptr, mmfs[i].size))
-			return error("Cannot merge binary files: %s",
-					argv[i]);
+			return ret;
 	}
 
 	xmp.ancestor = names[1];