Silence a warning about possible use of uninitialized variable

... when building in release mode. There isn't an actual problem - the
initialization and the use are guarded by the same condition.
Traverse block and function level function declarations during the
instrumentation of the containing function

The functions itself would be instrumented before compilation (usually
on the first call), however, when compiling the containing function, the
full compiler build the function info, which would contain a feedback
vector of the wrong (pre-instrumentation) length.