utils: validate allocation before filling with GUID on windows.

Signed-off-by: Phillip Whelan <phil@calyptia.com>

src/flb_utils.c

@@ -1415,12 +1415,13 @@ int flb_utils_get_machine_id(char **out_id, size_t *out_size)
 
     if (status == ERROR_SUCCESS) {
         *out_id = flb_calloc(1, dwBufSize+1);
-        memcpy(*out_id, buf, dwBufSize);
 
         if (*out_id == NULL) {
             return -1;
         }
 
+        memcpy(*out_id, buf, dwBufSize);
+
         /* RegQueryValueEx sets dwBufSize to strlen()+1 for the NULL 
          * terminator, but we only need strlen(). */
         *out_size = dwBufSize-1;