merge: clarify "pulling into void" special case

Instead of having it as one of the three if/elseif/.. case arms,
test the condition and handle this special case upfront.  This makes
it easier to follow the flow of logic.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/merge.c

@@ -1178,23 +1178,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_merge_usage,
 			builtin_merge_options);
 
-	/*
-	 * This could be traditional "merge <msg> HEAD <commit>..."  and
-	 * the way we can tell it is to see if the second token is HEAD,
-	 * but some people might have misused the interface and used a
-	 * commit-ish that is the same as HEAD there instead.
-	 * Traditional format never would have "-m" so it is an
-	 * additional safety measure to check for it.
-	 */
-
-	if (!have_message && head_commit &&
-	    is_old_style_invocation(argc, argv, head_commit->object.sha1)) {
-		strbuf_addstr(&merge_msg, argv[0]);
-		head_arg = argv[1];
-		argv += 2;
-		argc -= 2;
-		remoteheads = collect_parents(head_commit, &head_subsumed, argc, argv);
-	} else if (!head_commit) {
+	if (!head_commit) {
 		struct commit *remote_head;
 		/*
 		 * If the merged head is a valid one there is no reason
@@ -1217,6 +1201,23 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		update_ref("initial pull", "HEAD", remote_head->object.sha1,
 			   NULL, 0, UPDATE_REFS_DIE_ON_ERR);
 		goto done;
+	}
+
+	/*
+	 * This could be traditional "merge <msg> HEAD <commit>..."  and
+	 * the way we can tell it is to see if the second token is HEAD,
+	 * but some people might have misused the interface and used a
+	 * commit-ish that is the same as HEAD there instead.
+	 * Traditional format never would have "-m" so it is an
+	 * additional safety measure to check for it.
+	 */
+	if (!have_message &&
+	    is_old_style_invocation(argc, argv, head_commit->object.sha1)) {
+		strbuf_addstr(&merge_msg, argv[0]);
+		head_arg = argv[1];
+		argv += 2;
+		argc -= 2;
+		remoteheads = collect_parents(head_commit, &head_subsumed, argc, argv);
 	} else {
 		struct strbuf merge_names = STRBUF_INIT;