new compilation warning in 2.2.x branch

[Uwe Stöhr]

I found time to compile today's 2.2.x branch. I get this warning that 
could and should be avoided:

  TextMetrics.cpp
D:\LyXGit\2.2.x\src\RowPainter.cpp(590): warning C4244: 'initializing': 
conversion from 'double' to 'int', possible loss of data 
[D:\LyXGit\2.2.x\compile-2015\src\LyX.vcxproj]

regards Uwe