TgaImporter: more verbose error when image type is not supported.

src/Plugins/TgaImporter/Test/TgaImporterTest.cpp

@@ -108,7 +108,7 @@ void TgaImporterTest::compressed() {
     std::ostringstream debug;
     Error::setOutput(&debug);
     CORRADE_VERIFY(!importer.image2D(0));
-    CORRADE_COMPARE(debug.str(), "Trade::TgaImporter::TgaImporter::image2D(): compressed files are not supported\n");
+    CORRADE_COMPARE(debug.str(), "Trade::TgaImporter::TgaImporter::image2D(): unsupported (compressed?) image type: 9\n");
 }
 
 void TgaImporterTest::colorBits16() {

src/Plugins/TgaImporter/TgaImporter.cpp

@@ -133,7 +133,7 @@ ImageData2D* TgaImporter::image2D(UnsignedInt id) {
 
     /* Compressed files */
     } else {
-        Error() << "Trade::TgaImporter::TgaImporter::image2D(): compressed files are not supported";
+        Error() << "Trade::TgaImporter::TgaImporter::image2D(): unsupported (compressed?) image type:" << header.imageType;
         return nullptr;
     }