Allow NQ's SV_RunThink to loop.

This brings NQ's physics a little closer to QW's. After studying both the
original WinQuake source and the progs source, this change should be
harmless, making very little difference. However, it does allow an
entity's think function to be called multiple times in the same frame (for
when the entity needs more time to think, but it would cause runaway loop
errors). Maybe need a "runaway think" check.

nq/source/sv_phys.c

@@ -148,7 +148,7 @@ SV_RunThink (edict_t *ent)
 
 		if (ent->free)
 			return false;
-	} while (0);
+	} while (1);
 
 	return true;
 }