5505: FP: Array accessed out of bounds

CheckBufferOverrun::checkFunctionParameter alreacy considered usage of a
function parameter inside an if block as a special case.

With the patch the same is done for switch statements.

A test is added.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Merge pull request #256 from xypron/5505

5505: FP: Array accessed out of bounds