fix dollar escape in TEXT

The idea found in the code is any double dollar ($$) is being treated as
explicit dollar sign ($) instead of the start of a text object
reference. Due to missing update of the 's' variable, when creating a
text object for the text following the second dollar sign, the later was
prepended, leading to a double dollar in the output.

src/conky.c

@@ -2844,6 +2844,7 @@ static int extract_variable_text_internal(struct text_object *retval, const char
 				continue;
 			} else {
 				obj = create_plain_text("$");
+				s = p + 1;
 				if (obj != NULL) {
 					append_object(retval, obj);
 				}