util: make calling remove_from_list multiple times in a row safe

This commit fixes an infinite loop in foreach_s if remove_from_list is used
more than once on the same item with other list operations in between.

NOTE: This is a candidate for the 7.9 branch because the commit
"r300g: fixup long-lived BO maps being incorrectly unmapped when flushing"
depends on it.

src/gallium/auxiliary/util/u_simple_list.h

@@ -46,6 +46,8 @@
 do {						\
    (elem)->next->prev = (elem)->prev;		\
    (elem)->prev->next = (elem)->next;		\
+   (elem)->next = elem;                         \
+   (elem)->prev = elem;                         \
 } while (0)
 
 /**