Fix missing return after %submit is rejected

Using %submit is currently only allowed if the caller has
Submit granted on refs/for/$branch. Early return once it
is known submit permission is missing.

Change-Id: I8da76454bf1efdf9fbc9ec662e1711489dbce009

gerrit-server/src/main/java/com/google/gerrit/server/git/ReceiveCommits.java

@@ -1315,6 +1315,7 @@ public class ReceiveCommits {
     if (magicBranch.isSubmit() && !projectControl.controlForRef(
         MagicBranch.NEW_CHANGE + ref).canSubmit()) {
       reject(cmd, "submit not allowed");
+      return;
     }
 
     RevWalk walk = rp.getRevWalk();