Fix FTBFS if no "-e" parameter is used

diff --git a/configure.py b/configure.py
index 4af4e9b..d719b13 100644
--- a/configure.py
+++ b/configure.py
@@ -836,6 +836,8 @@
     global pytde_imports, kde_includes
     global opt_libpython
 
+    opt_libpython = None
+
     # Look for '-z' first and process that switch
     # (command line switches override file switches)
     for opt, arg in optlist: