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 :-)


git-svn-id: svn://svn.tartarus.org/sgt@10196 cda61777-01e9-0310-a592-d414129be87e