force creation of std::exception early

`std::exception` is supposed to inherit from `BaseException`
if other classes that inherit `std::exception` are created first,
then the Python wrapper class of `std::exception` no longer inherits `BaseException`

Author: Vipul-Cariappa

python/cppyy/__init__.py

@@ -85,6 +85,10 @@ def _set_pch():
 sys.modules['cppyy.gbl.std'] = gbl.std
 
 
+#- force creation of std.exception -------------------------------------------------------
+_e = gbl.std.exception
+
+
 #- enable auto-loading -------------------------------------------------------
 try:    gbl.cling.runtime.gCling.EnableAutoLoading()
 except: pass