test: fix common.mustCall
test: fix common.mustCall

Don't run the 'has function been called?' checks if the test is exiting
with an error because a failed check will mask the real exception.

v0.8 doesn't have the _fatalException machinery in src/node.js and
src/node.cc so it doesn't have this issue.

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node