STYLE: check autoPtr as plain bool instead of valid()

- cleaner code, more similarity with unique_ptr

  Now
      if (ptr)
      if (!ptr)

  instead
      if (ptr.valid())
      if (!ptr.valid())

applications/utilities/miscellaneous/foamFormatConvert/foamFormatConvert.C

@@ -426,9 +426,9 @@ int main(int argc, char *argv[])
 
         if (!lagrangianDirs.empty())
         {
-            if (meshPtr.valid())
+            if (meshPtr)
             {
-                meshPtr().readUpdate();
+                meshPtr->readUpdate();
             }
             else
             {