Avoid GC run between mysql_stmt_execute and mysql_stmt_store_result

This fixes a regression caused by brianmario#912 due to calling `rb_funcall`
between `mysql_stmt_execute` and `mysql_stmt_store_result`, it will
cause `mysql_stmt_close` to be called in wrong order.

Fixes brianmario#956.

ext/mysql2/statement.c

@@ -426,12 +426,12 @@ static VALUE rb_mysql_stmt_execute(int argc, VALUE *argv, VALUE self) {
   (void)RB_GC_GUARD(current);
   Check_Type(current, T_HASH);
 
-  // Merge in hash opts/keyword arguments
-  if (!NIL_P(opts)) {
-    rb_funcall(current, intern_merge_bang, 1, opts);
+  is_streaming = (Qtrue == rb_hash_aref(current, sym_stream));
+
+  if (!is_streaming && !NIL_P(opts)) {
+    is_streaming = (Qtrue == rb_hash_aref(opts, sym_stream));
   }
 
-  is_streaming = (Qtrue == rb_hash_aref(current, sym_stream));
   if (!is_streaming) {
     // recieve the whole result set from the server
     if (mysql_stmt_store_result(stmt)) {
@@ -441,6 +441,11 @@ static VALUE rb_mysql_stmt_execute(int argc, VALUE *argv, VALUE self) {
     wrapper->active_thread = Qnil;
   }
 
+  // Merge in hash opts/keyword arguments
+  if (!NIL_P(opts)) {
+    rb_funcall(current, intern_merge_bang, 1, opts);
+  }
+
   resultObj = rb_mysql_result_to_obj(stmt_wrapper->client, wrapper->encoding, current, metadata, self);
 
   rb_mysql_set_server_query_flags(wrapper->client, resultObj);