Avoid needless second string conversion when adding files to memory FS.

Create the buffer holding the result of conversion instead of converting
twice, once to only get the length of the result and the second time to get
the data.

Closes #13877.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70392 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/fs_mem.cpp

@@ -186,13 +186,9 @@ void wxMemoryFSHandlerBase::AddFileWithMimeType(const wxString& filename,
                                                 const wxString& textdata,
                                                 const wxString& mimetype)
 {
-    AddFileWithMimeType
-    (
-        filename,
-        static_cast<const char *>(textdata.To8BitData()),
-        wxStrlen(static_cast<const char *>(textdata.To8BitData())),
-        mimetype
-    );
+    const wxCharBuffer buf(textdata.To8BitData());
+
+    AddFileWithMimeType(filename, buf.data(), buf.length(), mimetype);
 }