Small irgen fix

Should probably nuke all of the codegen "memory management" using vrefs,
and instead just used shared_pointers.  Looks like there could be more
"bugs" of the kind fixed in this commit...

src/codegen/irgen/irgenerator.cpp

@@ -598,6 +598,8 @@ private:
                 llvm::Value* v = i1FromBool(emitter, rtn);
                 assert(v->getType() == g.i1);
 
+                obj->decvref(emitter);
+
                 return boolFromI1(emitter, v);
             }
             case AST_LangPrimitive::SET_EXC_INFO: {

test/tests/control_flow.py

+# Random regression test:
+
+def _escape():
+    code = DOESNT_EXIST
+    if code:
+        return code
+
+_escape()