Fix build with wxUSE_FFILE=0.

Add the missing "#if wxUSE_FFILE" checks and add fallbacks to wxFile if it's
available.

Closes #15353.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74596 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/textcmn.cpp

@@ -915,6 +915,8 @@ bool wxTextAreaBase::DoLoadFile(const wxString& filename, int WXUNUSED(fileType)
             return true;
         }
     }
+#else
+    (void)filename;   // avoid compiler warning about unreferenced parameter
 #endif // wxUSE_FFILE
 
     wxLogError(_("File couldn't be loaded."));
@@ -936,6 +938,8 @@ bool wxTextAreaBase::DoSaveFile(const wxString& filename, int WXUNUSED(fileType)
 
         return true;
     }
+#else
+    (void)filename;   // avoid compiler warning about unreferenced parameter
 #endif // wxUSE_FFILE
 
     return false;