Abstract binary blob loading to FileSystemUtils

This seems to be a comment left by Ethan that he never got around to. So
I did it for him.

What I've done is made it so FileSystemUtils.cpp knows what a binary
blob is, and moved the binary blob loading code directly to
FileSystemUtils.cpp. To do this, I removed the private access modifier
from binaryBlob - I don't think we'll need it, and anyways when we move
to C we can't use it.

Along the way, I also cleaned up the style of the function a bit - the
null termination offset is no longer hardcoded, and the function no
longer mixes code and declarations together in the same block.

I also noticed that when printing all the filenames at the end, a single
invalid header would stop the whole loop instead of just being skipped
over... this seems to be a bug to me, so I've made it so invalid headers
just get skipped over instead of stopping the whole loop.

In FileSystemUtils.h, I used a forward declaration. In hindsight,
incomplete forward declarations should basically always be done in
header files if possible, otherwise this introduces the possibility of
transitive includes - if a file includes this header and it does a full
include, the file is silently able to use the full header, whereas if
it's a forward declaration, then the moment the file tries to use the
full header it fails, and then it's forced to include the full header
for itself. But uh, that's a code cleanup for later.

desktop_version/src/FileSystemUtils.h

@@ -1,6 +1,9 @@
 #ifndef FILESYSTEMUTILS_H
 #define FILESYSTEMUTILS_H
 
+/* Forward declaration */
+class binaryBlob;
+
 #include <stddef.h>
 
 // Forward declaration, including the entirety of tinyxml2.h across all files this file is included in is unnecessary
@@ -29,6 +32,9 @@ void FILESYSTEM_loadAssetToMemory(
     const bool addnull
 );
 void FILESYSTEM_freeMemory(unsigned char **mem);
+
+bool FILESYSTEM_loadBinaryBlob(binaryBlob* blob, const char* filename);
+
 bool FILESYSTEM_saveTiXml2Document(const char *name, tinyxml2::XMLDocument& doc);
 bool FILESYSTEM_loadTiXml2Document(const char *name, tinyxml2::XMLDocument& doc);