mingw doesn't like __int64 left alone (probably #define'd instead typedef'ed)

git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@5179 212acab6-be3b-0410-9dea-997c60f758d6

Contrib/NSISdl/httpget.cpp

@@ -493,5 +493,5 @@ __int64 JNL_HTTPGet::content_length()
   // some buggy apache servers return negative values for sizes
   // over 2gb - fix it for them
   if (cl < 0)
-    return __int64(unsigned(cl));
+    return (__int64)((unsigned int)(cl));
 }