Fix -Wmaybe-uninitialized in TimeCache

Author: gleichdick

tf2/src/cache.cpp

@@ -191,8 +191,8 @@ bool TimeCache::getData(
   std::string * error_str)
 {
   // returns false if data not available
-  TransformStorage * p_temp_1;
-  TransformStorage * p_temp_2;
+  TransformStorage * p_temp_1 = nullptr;
+  TransformStorage * p_temp_2 = nullptr;
 
   int num_nodes = findClosest(p_temp_1, p_temp_2, time, error_str);
   if (num_nodes == 0) {