Fix vertically misaligned text in Javascript puzzles.

Fix vertically misaligned text in Javascript puzzles.

When I constructed my test canvas to measure the vertical extent of a
text string for ALIGN_VCENTRE, I forgot to ensure that the 'width'
variable was an integer, as a result of which the loop over canvas
pixels kept trying to use fractional array indices and returning
undefined :-)

[originally from svn r10196]