xmlreader.cpp: using 'else if' after return is faster than 'if'

Performance testing indicates that:

         if (...) return ...;
    else if (...) return ...;

can be optimized better than:

    if (...) return ...;
    if (...) return ...;

Before : 0.1325 (standard deviation = 0.0037)
After  : 0.1319 (standard deviation = 0.0030)