fix(exr): allow an empty "name" metadata to be read (#4528)

When the exr "name" metadata (used for the names of subimages/parts)
existed but was the empty string, we were treating it like it didn't
exist (and upon write substituted our own "subimageXY" name, as we are
wont to do for unnamed parts). But now we've seen multi-part exrs where
the name is "" (exists, but empty string) and we want a read-write cycle
to preserve that. Even though it's not a very sensible or helpful part
name, it's technically legal, so we should honor it.

Signed-off-by: Larry Gritz <[email protected]>

src/openexr.imageio/exrinput.cpp

@@ -652,7 +652,7 @@ OpenEXRInput::PartInfo::parse_header(OpenEXRInput* in,
     }
 
     // EXR "name" also gets passed along as "oiio:subimagename".
-    if (header->hasName() && header->name() != "")
+    if (header->hasName())
         spec.attribute("oiio:subimagename", header->name());
 
     spec.attribute("oiio:subimages", in->m_nsubimages);