fixed a bug in create collection in cluster, where transaction result was not checked for success before access (#3137)

arangod/Agency/State.cpp

@@ -246,7 +246,6 @@ index_t State::log(query_t const& transactions, size_t ndups) {
   TRI_ASSERT(nqs > ndups);
 
   MUTEX_LOCKER(mutexLocker, _logLock);  // log entries must stay in order
-  std::string clientId;
 
   for (size_t i = ndups; i < nqs; ++i) {
     VPackSlice const& slice = slices[i];

arangod/Cluster/ClusterInfo.cpp

@@ -1321,7 +1321,6 @@ int ClusterInfo::createCollectionCoordinator(std::string const& databaseName,
     MUTEX_LOCKER(locker, *cacheMutex);
 
     auto res = ac.sendTransactionWithFailover(transaction);
-    auto result = res.slice();
 
     // Only if not precondition failed
     if (!res.successful()) {
@@ -1329,6 +1328,7 @@ int ClusterInfo::createCollectionCoordinator(std::string const& databaseName,
           (int)arangodb::rest::ResponseCode::PRECONDITION_FAILED) {
         AgencyCommResult ag = ac.getValues("/");
 
+        auto result = res.slice();
         if (result.isArray() && result.length() > 0) {
           if (result[0].isObject()) {
             auto tres = result[0];
@@ -1761,7 +1761,7 @@ int ClusterInfo::ensureIndexCoordinator(
       }
     }
 
-    if (!planValue) {
+    if (planValue==nullptr) {
       // hmm :S both empty :S did somebody else clean up? :S
       // should not happen?
       return errorCode;

arangod/Cluster/ClusterMethods.cpp

@@ -893,7 +893,6 @@ int selectivityEstimatesOnCoordinator(
             if(identifier.value.hasKey("selectivityEstimate")) {
               StringRef shard_index_id(identifier.key);
               auto split_point = std::find(shard_index_id.begin(), shard_index_id.end(),'/');
-              std::string shard(shard_index_id.begin(), split_point );
               std::string index(split_point + 1, shard_index_id.end());
 
               double estimate = arangodb::basics::VelocyPackHelper::getNumericValue(