mesa/vbo: fix compile and replay of nodes ending in a FALLBACK

mesa/vbo: fix compile and replay of nodes ending in a FALLBACK

Where vbo save nodes are terminated with a call to DO_FALLBACK(), as in
the case of a recursive CallList which is itself within a Begin/End pair,
there two problems:
1) The display list node's primitive information was incorrect, stating
the cut-off prim had zero vertices
2) On replay, we would get confused by a primitive that started in a
node, but was terminated by individual opcodes.

This change fixes the first problem by correctly terminating the last
primitive on fallback, and the second by forcing the display list to
use the Loopback path, converting all nodes into immediate-mode rendering.

The loopback fix is a performance hit, but avoiding this would require
a fairly large rework of this code.