ControlFlowAnalyser: Also consider called functions in a flow

test/libsolidity/syntaxTests/controlFlow/uninitializedAccess/reverting_call_virtual.sol

@@ -0,0 +1,27 @@
+abstract contract B
+{
+        function iWillRevert() pure public virtual { revert(); }
+
+        function test2(bool _param) pure external returns(uint256)
+        {
+                if (_param) return 1;
+
+                iWillRevert();
+        }
+}
+
+contract C is B
+{
+        function iWillRevert() pure public override {  }
+
+        function test(bool _param) pure external returns(uint256)
+        {
+                if (_param) return 1;
+
+                iWillRevert();
+        }
+}
+
+// ----
+// Warning 6321: (146-153): Unnamed return variable can remain unassigned when the function is called when "C" is the most derived contract. Add an explicit return with value to all non-reverting code paths or name the variable.
+// Warning 6321: (381-388): Unnamed return variable can remain unassigned. Add an explicit return with value to all non-reverting code paths or name the variable.