LibVNCClient: make sure Ultra decoding cannot dereference a null pointer

Closes #254

libvncclient/ultra.c

@@ -66,6 +66,8 @@ HandleUltraBPP (rfbClient* client, int rx, int ry, int rw, int rh)
     if ((client->raw_buffer_size % 4)!=0)
       client->raw_buffer_size += (4-(client->raw_buffer_size % 4));
     client->raw_buffer = (char*) malloc( client->raw_buffer_size );
+    if(client->raw_buffer == NULL)
+      return FALSE;
   }
   
   /* allocate enough space to store the incoming compressed packet */
@@ -150,6 +152,8 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
     if ((client->raw_buffer_size % 4)!=0)
       client->raw_buffer_size += (4-(client->raw_buffer_size % 4));
     client->raw_buffer = (char*) malloc( client->raw_buffer_size );
+    if(client->raw_buffer == NULL)
+	return FALSE;
   }