Add fallthrough comment to switch case

This allows gcc to identify intentional fallthroughs, which are part all
-Wall. Specifically -Werror=implicit-fallthrough

code/AssetLib/3DS/3DSConverter.cpp

@@ -262,7 +262,7 @@ void Discreet3DSImporter::ConvertMaterial(D3DS::Material &oldMat,
         unsigned int iWire = 1;
         mat.AddProperty<int>((int *)&iWire, 1, AI_MATKEY_ENABLE_WIREFRAME);
     }
-
+// fallthrough
     case D3DS::Discreet3DS::Gouraud:
         eShading = aiShadingMode_Gouraud;
         break;

code/AssetLib/3DS/3DSLoader.cpp

@@ -1284,7 +1284,7 @@ void Discreet3DSImporter::ParseColorChunk(aiColor3D *out, bool acceptPercent) {
     switch (chunk.Flag) {
     case Discreet3DS::CHUNK_LINRGBF:
         bGamma = true;
-
+    // fallthrough
     case Discreet3DS::CHUNK_RGBF:
         if (sizeof(float) * 3 > diff) {
             *out = clrError;
@@ -1297,6 +1297,7 @@ void Discreet3DSImporter::ParseColorChunk(aiColor3D *out, bool acceptPercent) {
 
     case Discreet3DS::CHUNK_LINRGBB:
         bGamma = true;
+            // fallthrough
     case Discreet3DS::CHUNK_RGBB: {
         if (sizeof(char) * 3 > diff) {
             *out = clrError;

code/AssetLib/ASE/ASELoader.cpp

@@ -870,6 +870,7 @@ void ASEImporter::ConvertMaterial(ASE::Material &mat) {
         unsigned int iWire = 1;
         mat.pcInstance->AddProperty<int>((int *)&iWire, 1, AI_MATKEY_ENABLE_WIREFRAME);
     }
+    // fallthrough
     case D3DS::Discreet3DS::Gouraud:
         eShading = aiShadingMode_Gouraud;
         break;

code/AssetLib/LWO/LWOLoader.cpp

@@ -1540,6 +1540,7 @@ void LWOImporter::LoadLWO2File() {
                     break;
                 }
                 // --- intentionally no break here
+                // fallthrough
             case AI_LWO_VMAP: {
                 if (skip)
                     break;