Revert part of last commit unsuitable for older compilers (#3584)

Also initialise all the items in gResearchedTrackTypesA and
gResearchedTrackTypesB

src/rct2/S6Importer.cpp

@@ -50,6 +50,7 @@ public:
 S6Importer::S6Importer()
 {
     FixIssues = false;
+    memset(&_s6, 0, sizeof(_s6));
 }
 
 void S6Importer::LoadSavedGame(const utf8 * path)

src/rct2/S6Importer.h

@@ -41,6 +41,6 @@ public:
 
 private:
     const utf8 * _s6Path = nullptr;
-    rct_s6_data  _s6 = { 0 };
+    rct_s6_data  _s6;
     uint8        _gameVersion = 0;
 };

src/windows/editor_bottom_toolbar.c

@@ -249,6 +249,11 @@ static void sub_66F6E3()
 		gResearchedTrackTypesB[i] = (RideTypePossibleTrackConfigurations[i] >> 32ULL) & 0xFFFFFFFFULL;
 	}
 
+	for (int i = countof(RideTypePossibleTrackConfigurations); i < 128; i++) {
+		gResearchedTrackTypesA[i] = (uint32)-1;
+		gResearchedTrackTypesB[i] = (uint32)-1;
+	}
+
 	for (int i = 0; i < 8; i++) {
 		gResearchedRideEntries[i] = 0xFFFFFFFF;
 	}

src/windows/editor_object_selection.c

@@ -1943,6 +1943,12 @@ static void window_editor_object_selection_manage_tracks()
 		gResearchedTrackTypesB[i] = (RideTypePossibleTrackConfigurations[i] >> 32ULL) & 0xFFFFFFFFULL;
 	}
 
+
+	for (int i = countof(RideTypePossibleTrackConfigurations); i < 128; i++) {
+		gResearchedTrackTypesA[i] = (uint32)-1;
+		gResearchedTrackTypesB[i] = (uint32)-1;
+	}
+
 	for (int i = 0; i < 8; i++) {
 		gResearchedRideEntries[i] = 0xFFFFFFFF;
 	}