compext/Png.c: simplify srcBuf allocation

nx-X11/programs/Xserver/hw/nxagent/compext/Png.c

@@ -481,17 +481,26 @@ char *PngCompressData(XImage *image, int *compressed_size)
     return NULL;
   }
 
+  int count;
   if (color_type == PNG_COLOR_TYPE_PALETTE)
   {
-    srcBuf = (CARD8 *) malloc(w * sizeof(CARD8));
+    count = w;
+  }
+  else
+  {
+    count = 3 * w;
+  }
+
+  srcBuf = (CARD8 *) calloc(count, sizeof(CARD8));
 
   if (srcBuf == NULL)
   {
     #ifdef PANIC
     fprintf(stderr, "******PngCompressData: PANIC! Cannot allocate [%d] bytes.\n",
-                  (int) (w * sizeof(CARD8)));
+                  (int) (count * sizeof(CARD8)));
     #endif
 
+    free(pngCompBuf);
     free(image_index);
 
     return NULL;
@@ -504,32 +513,6 @@ char *PngCompressData(XImage *image, int *compressed_size)
    * at the end of the procedure.
    */
 
-    memset(srcBuf, 0, w * sizeof(CARD8));
-  }
-  else
-  {
-    srcBuf = (CARD8 *) malloc(w * 3 * sizeof(CARD8));
-
-    /*
-     * TODO: See above.
-     */
-
-    memset(srcBuf, 0, w * 3 * sizeof(CARD8));
-  }
-
-  if (srcBuf == NULL)
-  {
-    #ifdef PANIC
-    fprintf(stderr, "******PngCompressData: PANIC! Cannot allocate [%d] bytes.\n",
-                w * 3);
-    #endif
-
-    free(pngCompBuf);
-    free(image_index);
-
-    return NULL;
-  }
-
   for (dy = 0; dy < h; dy++)
   {
     if (color_type == PNG_COLOR_TYPE_RGB)