Python: Ignore .isAbsent() from ClassCall

This means that DataFlowCall is only for resolvable calls, which might not seem
like a big thing in itself, but enables the next commit to actually work :P

Author: RasmusWL

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPrivate.qll

@@ -704,7 +704,7 @@ newtype TDataFlowCall =
   TFunctionCall(CallNode call) { call = any(FunctionValue f).getAFunctionCall() } or
   /** Bound methods need to make room for the explicit self parameter */
   TMethodCall(CallNode call) { call = any(FunctionValue f).getAMethodCall() } or
-  TClassCall(CallNode call) { call = any(ClassValue c).getACall() } or
+  TClassCall(CallNode call) { call = any(ClassValue c | not c.isAbsent()).getACall() } or
   TSpecialCall(SpecialMethodCallNode special)
 
 /** Represents a call. */

python/ql/test/experimental/dataflow/calls/test.py

@@ -31,7 +31,7 @@ def __getitem__(self, key):
     # `mypkg.foo` is a `missing module variable`, but `mypkg.subpkg.bar` is compeltely
     # ignored.
     import mypkg
-    mypkg.foo(42) # $ call=mypkg.foo(..) qlclass=ClassCall arg_0=[pre]mypkg.foo(..)
+    mypkg.foo(42)
     mypkg.subpkg.bar(43)
 except:
     pass