Fix: Protect against a few out of bounds or uninitialised usage errors

src/pathfinder/opf/opf_ship.cpp

@@ -145,6 +145,7 @@ static uint FindShipTrack(const Ship *v, TileIndex tile, DiagDirection dir, Trac
 
 	Track best_track = INVALID_TRACK;
 
+	assert(bits != TRACK_BIT_NONE);
 	do {
 		Track i = RemoveFirstTrack(&bits);
 
@@ -176,7 +177,7 @@ good:;
 		best_length = pfs.best_length;
 bad:;
 
-	} while (bits != 0);
+	} while (bits != TRACK_BIT_NONE);
 
 	*track = best_track;
 	return best_bird_dist;

src/pathfinder/yapf/yapf_rail.cpp

@@ -28,6 +28,8 @@ template <typename Tpf> void DumpState(Tpf &pf1, Tpf &pf2)
 	pf2.DumpBase(dmp2);
 	FILE *f1 = fopen("yapf1.txt", "wt");
 	FILE *f2 = fopen("yapf2.txt", "wt");
+	assert(f1 != NULL);
+	assert(f2 != NULL);
 	fwrite(dmp1.m_out.Data(), 1, dmp1.m_out.Size(), f1);
 	fwrite(dmp2.m_out.Data(), 1, dmp2.m_out.Size(), f2);
 	fclose(f1);