- uncoupled the decompressors from ZDoom's internal error handling.

This code made it hard to repurpose this code for other tools, so now the error handler must be passed as a callback to OpenDecompressor.

src/utility/cmdlib.cpp

@@ -995,3 +995,33 @@ bool IsAbsPath(const char *name)
 #endif /* _WIN32 */
     return 0;
 }
+
+//
+// M_ZlibError
+//
+FString M_ZLibError(int zerr)
+{
+	if (zerr >= 0)
+	{
+		return "OK";
+	}
+	else if (zerr < -6)
+	{
+		FString out;
+		out.Format("%d", zerr);
+		return out;
+	}
+	else
+	{
+		static const char* errs[6] =
+		{
+			"Errno",
+			"Stream Error",
+			"Data Error",
+			"Memory Error",
+			"Buffer Error",
+			"Version Error"
+		};
+		return errs[-zerr - 1];
+	}
+}