range-diff: plug memory leak in common invocation

Create a public release_patch() version of the private free_patch()
function added in 13b5af22f3 (apply: move libified code from
builtin/apply.c to apply.{c,h}, 2016-04-22). Unlike the existing
function this one doesn't free() the "struct patch" itself, so we can
use it for variables on the stack.

Use it in range-diff.c to fix a memory leak in common range-diff
invocations, e.g.:

    git -P range-diff origin/master origin/next origin/seen

Would emit several errors when compiled with SANITIZE=leak, but now
runs cleanly.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

apply.c

@@ -219,13 +219,18 @@ static void free_fragment_list(struct fragment *list)
 	}
 }
 
-static void free_patch(struct patch *patch)
+void release_patch(struct patch *patch)
 {
 	free_fragment_list(patch->fragments);
 	free(patch->def_name);
 	free(patch->old_name);
 	free(patch->new_name);
 	free(patch->result);
+}
+
+static void free_patch(struct patch *patch)
+{
+	release_patch(patch);
 	free(patch);
 }
 

apply.h

@@ -173,6 +173,8 @@ int parse_git_diff_header(struct strbuf *root,
 			  unsigned int size,
 			  struct patch *patch);
 
+void release_patch(struct patch *patch);
+
 /*
  * Some aspects of the apply behavior are controlled by the following
  * bits in the "options" parameter passed to apply_all_patches().

range-diff.c

@@ -165,6 +165,7 @@ static int read_patches(const char *range, struct string_list *list,
 					    patch.old_mode, patch.new_mode);
 
 			strbuf_addstr(&buf, " ##");
+			release_patch(&patch);
 		} else if (in_header) {
 			if (starts_with(line, "Author: ")) {
 				strbuf_addstr(&buf, " ## Metadata ##\n");