Fix vivien#146: Colors key has no effect.

The original mantainer did not add the patch, so I had to fork it and
apply the patch myself.
the patch is mentioned already in issue#146:
vivien#146

src/block.c

@@ -163,7 +163,8 @@ block_update_plain_text(struct block *block, char *buf)
                 return;
 
 	linecpy(&lines, props->short_text, sizeof(props->short_text) - 1);
-	linecpy(&lines, props->color, sizeof(props->color) - 1);
+	if (*lines)
+		linecpy(&lines, props->color, sizeof(props->color) - 1);
 }
 
 static void