Fix error reporting for wxCopyFile() under Unix

Check if copying file actually succeeded, any IO errors that could happen in
it were previously just completely ignored.

See #17638.

(cherry picked from commit a93dcc531c)

src/common/filefn.cpp

@@ -1092,7 +1092,11 @@ wxCopyFile (const wxString& file1, const wxString& file2, bool overwrite)
         return false;
     }
 
-    wxDoCopyFile(fileIn, fbuf, file2, overwrite);
+    if ( !wxDoCopyFile(fileIn, fbuf, file2, overwrite) )
+    {
+        wxLogError(_("Error copying the file '%s' to '%s'."), file1, file2);
+        return false;
+    }
 
 #if defined(__WXMAC__) || defined(__WXCOCOA__)
     // copy the resource fork of the file too if it's present