Revert "small addition to the bugfix for #1336, avoiding NPE"

This reverts commit c52e5a7.

Author: danielgrahl

system/src/de/uka/ilkd/key/proof/Goal.java

@@ -621,7 +621,7 @@ public ImmutableList<Goal> apply( RuleApp p_ruleApp ) {
                 MatchConditions newConditions = rwt.checkPrefix(ruleApp.posInOccurrence(),
                         MatchConditions.EMPTY_MATCHCONDITIONS, proof.getServices());
                 if(newConditions == null) {
-                    throw new RuntimeException("taclet application with unsatisfied 'checkPrefix': " 
+                    throw new RuntimeException("taclet application with unsatisfied 'checkPrefix': "
                             + ruleApp);
                 }
 

system/src/de/uka/ilkd/key/strategy/TacletAppContainer.java

@@ -318,7 +318,7 @@ public RuleApp completeRuleApp(Goal p_goal, Strategy strategy) {
         if ( !app.complete() )
             app = app.tryToInstantiate ( services );
 
-        Taclet taclet = app.taclet();
+        Taclet taclet = app == null ? null : app.taclet();
         if (taclet instanceof RewriteTaclet) {
             RewriteTaclet rwtaclet = (RewriteTaclet) taclet;
             MatchConditions check =