MB-49040: 7/n Skip scope dataSize update for delta of 0

Simply check the delta value and return before we do a scope
lookup.

Change-Id: I7f7b31143b52b487a66567b3e471f488fea2920d
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/164632
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Paolo Cocchi <paolo.cocchi@couchbase.com>

engines/ep/src/collections/vbucket_manifest.cc

@@ -1024,6 +1024,11 @@ size_t Manifest::getDataSize(ScopeID sid) const {
 
 void Manifest::updateScopeDataSize(const container::const_iterator entry,
                                    ssize_t delta) const {
+    // Don't continue with a zero update, avoids scope map lookup
+    if (delta == 0) {
+        return;
+    }
+
     if (entry == map.end()) {
         throwException<std::invalid_argument>(__FUNCTION__,
                                               "iterator is invalid");