Always strip trailing separators from wxFileName::GetTempDir() under MSW.

In the unlikely but still possible case when neither TMP nor TEMP environment
variables are defined under Windows, we use the standard ::GetTempPath()
function which can return a path with trailing backslashes, e.g. if it takes
it from USERPROFILE environment variable. Ensure that these backslashes are
stripped in this case as well.

Closes https://github.com/wxWidgets/wxWidgets/pull/67

src/common/filename.cpp

@@ -1249,7 +1249,8 @@ wxString wxFileName::GetTempDir()
         dir = wxMacFindFolderNoSeparator(short(kOnSystemDisk), kTemporaryFolderType, kCreateFolder);
 #endif // systems with native way
     }
-    else // we got directory from an environment variable
+
+    if ( !dir.empty() )
     {
         // remove any trailing path separators, we don't want to ever return
         // them from this function for consistency
@@ -1266,7 +1267,7 @@ wxString wxFileName::GetTempDir()
     }
 
     // fall back to hard coded value
-    if ( dir.empty() )
+    else
     {
 #ifdef __UNIX_LIKE__
         dir = CheckIfDirExists("/tmp");