Test build: indirect draws checked before they run (#19)

Test build for #19. Not a release: the launcher does not offer it as an update. It is 0.51-linux.15 plus the Trophies fix from #22 and a check for indirect draws, waiting for testing.

Indirect draws checked before they run (#19). Some of the game's draws take their vertex and instance counts from memory a shader wrote. If those counts are garbage, the GPU can stay busy past the driver's limit and freeze (on NVIDIA, an Xid 109 in the kernel log). Before each such draw, the GPU now checks the counts and skips the draw if they are implausible. The game has only a handful of these draws per frame, so it costs nothing measurable.

If it catches anything, the log has a line starting with Indirect draws: … skipped. BB_INDIRECT_DRAW_GUARD=0 (in the launcher's extra variables) turns the check off.

What would help: play as usual, or where the game froze before, and attach the log (Advanced → Developer → Save the log and statistics to a file; it goes to ~/.local/share/bbport/logs).

SHA-256: b1376dcb31929f71ed63b53a702f6cb579568126656bd4bdc941382542f5d998