1) minor error handling improvements (was passing back invalid handle error, instead of the cause; also added a CHECK_ERR)

2) we attempt to load missing files (see bug #32). with the fix above,
CHECK_ERR would fire every run (which it should until the problem is
fixed :P), which is annoying.
Instead, FileUnpacker now checks if the file exists; if not, it throws
immediately and thereby bypasses the VFS error mechanism.

This was SVN commit r1503.

source/lib/res/tex.cpp

@@ -1174,8 +1174,7 @@ int tex_load(const char* fn, TexInfo* t)
 	void* _p = 0;
 	size_t size;
 	Handle hm = vfs_load(fn, _p, size);
-	if(hm <= 0)
-		return (int)hm;
+	CHECK_ERR(hm);	// (need handle below; can't test return value directly)
 	// guarantee *_valid routines 4 header bytes
 	if(size < 4)
 	{

source/lib/res/vfs.cpp

@@ -1672,6 +1672,10 @@ debug_out("vfs_load v_fn=%s\n", v_fn);
 	p = 0; size = 0;	// zeroed in case vfs_open or H_DEREF fails
 
 	Handle hf = vfs_open(v_fn, flags);
+	CHECK_ERR(hf);
+		// note: if we skip this and have H_DEREF report the error,
+		// we get "invalid handle" instead of vfs_open's error code.
+
 	H_DEREF(hf, VFile, vf);
 
 	Handle hm = 0;	// return value - handle to memory or error code

source/ps/FileUnpacker.cpp

@@ -26,6 +26,14 @@ CFileUnpacker::CFileUnpacker()
 // variety of exceptions for missing files etc
 void CFileUnpacker::Read(const char* filename,const char magicstr[4])
 {
+	// avoid vfs_load complaining about missing data files (which happens
+	// too often). better to check here than squelch internal VFS error
+	// reporting. we disable this in release mode to avoid a speed hit.
+#ifndef NDEBUG
+	if(!vfs_exists(filename))
+		throw CFileOpenError();
+#endif
+
 	// load the whole thing into memory
 	Handle hm = vfs_load(filename, m_Buf, m_Size);
 	if(hm <= 0)