Detect to variable declarations in conditions for CollapsibleIf check.

Verify if the ifStatement's condition is actually a variable declaration, as in :
    if (void * ptr = f()) {
    }

This prevents collapsing multiple if', since multiple definitions and expressions cannot be combined.
Merge pull request #190 from Typz/ifdeclaration

Detect to variable declarations in conditions for CollapsibleIf check.