ZDI-CAN-28158: use g_malloc0 instead of g_malloc

To avoid accessing uninitialized memory, replace calls to g_malloc with
g_malloc0 which initializes the allocated memory to zero.

plug-ins/common/file-pnm.c

@@ -693,7 +693,7 @@ load_image (GFile   *file,
     return NULL;
 
   /* allocate the necessary structures */
-  pnminfo = g_new (PNMInfo, 1);
+  pnminfo = g_new0 (PNMInfo, 1);
 
   pnminfo->tupltype = NULL;