Fix wxWidgets compilation issue.

wxFileName::GetAbsolutePath was introduced in 3.1.6:
https://docs.wxwidgets.org/3.2.2/classwx_file_name.html#a5ca18cc7b7af3d88a850fad22f993061

This patch is equivalent to the current code:
d39aac0fa8/include/wx/filename.h (L390)

common/eda_doc.cpp

@@ -145,7 +145,8 @@ bool GetAssociatedDocument( wxWindow* aParent, const wxString& aDocName, PROJECT
     wxFileName currentFileName( fullfilename );
 
     // Use wxWidgets to resolve any "." and ".." in the path
-    fullfilename = currentFileName.GetAbsolutePath();
+    currentFileName.MakeAbsolute();
+    fullfilename = currentFileName.GetFullPath();
 
     wxString file_ext = currentFileName.GetExt();