replace switch with if/return

Fixes warning C4702: unreachable code

No other way to make all compilers gappy.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/image.cpp

@@ -733,19 +733,15 @@ AccessMode ImageFactory::checkMode(ImageType type, MetadataId metadataId) {
   auto r = Exiv2::find(registry, type);
   if (!r)
     throw Error(ErrorCode::kerUnsupportedImageType, static_cast<int>(type));
-  switch (metadataId) {
-    case mdExif:
+  if (metadataId == mdExif)
     return r->exifSupport_;
-    case mdIptc:
+  if (metadataId == mdIptc)
     return r->iptcSupport_;
-    case mdXmp:
+  if (metadataId == mdXmp)
     return r->xmpSupport_;
-    case mdComment:
+  if (metadataId == mdComment)
     return r->commentSupport_;
-    default:
   return amNone;
-  }
-  return {};
 }
 
 bool ImageFactory::checkType(ImageType type, BasicIo& io, bool advance) {