change `git_config()` return value to void

Currently `git_config()` returns an integer signifying an error code.
During rewrites of the function most of the code was shifted to
`git_config_with_options()`. `git_config_with_options()` normally
returns positive values if its `config_source` parameter is set as NULL,
as most errors are fatal, and non-fatal potential errors are guarded
by "if" statements that are entered only when no error is possible.

Still a negative value can be returned in case of race condition between
`access_or_die()` & `git_config_from_file()`. Also, all callers of
`git_config()` ignore the return value except for one case in branch.c.

Change `git_config()` return value to void and make it die if it receives
a negative value from `git_config_with_options()`.

Original-patch-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Tanay Abhra <tanayabh@gmail.com>
Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

branch.c

@@ -161,10 +161,7 @@ int read_branch_desc(struct strbuf *buf, const char *branch_name)
 	strbuf_addf(&name, "branch.%s.description", branch_name);
 	cb.config_name = name.buf;
 	cb.value = NULL;
-	if (git_config(read_branch_desc_cb, &cb) < 0) {
-		strbuf_release(&name);
-		return -1;
-	}
+	git_config(read_branch_desc_cb, &cb);
 	if (cb.value)
 		strbuf_addstr(buf, cb.value);
 	strbuf_release(&name);

cache.h

@@ -1294,7 +1294,7 @@ extern int git_config_from_buf(config_fn_t fn, const char *name,
 			       const char *buf, size_t len, void *data);
 extern void git_config_push_parameter(const char *text);
 extern int git_config_from_parameters(config_fn_t fn, void *data);
-extern int git_config(config_fn_t fn, void *);
+extern void git_config(config_fn_t fn, void *);
 extern int git_config_with_options(config_fn_t fn, void *,
 				   struct git_config_source *config_source,
 				   int respect_includes);

config.c

@@ -1232,9 +1232,21 @@ int git_config_with_options(config_fn_t fn, void *data,
 	return ret;
 }
 
-int git_config(config_fn_t fn, void *data)
+void git_config(config_fn_t fn, void *data)
 {
-	return git_config_with_options(fn, data, NULL, 1);
+	if (git_config_with_options(fn, data, NULL, 1) < 0)
+		/*
+		 * git_config_with_options() normally returns only
+		 * positive values, as most errors are fatal, and
+		 * non-fatal potential errors are guarded by "if"
+		 * statements that are entered only when no error is
+		 * possible.
+		 *
+		 * If we ever encounter a non-fatal error, it means
+		 * something went really wrong and we should stop
+		 * immediately.
+		 */
+		die(_("unknown error occured while reading the configuration files"));
 }
 
 static struct config_set_element *configset_find_element(struct config_set *cs, const char *key)