Fix a small untracked bug

where the cursor would stay on the very last frame (again, a rogue '<' instead of '<=')
Fixes part of #95

the "overflow" is fixed, instead now the cursor "stays behind"...
Fix another part of #95

but now future frames get colored "unloaded" when mouse-overing them
Completely fixes #95.

I don't see any more bugs in the preload indicator mouseover...
Nicer syntax for parseInt("")-protection

As suggested by MaPePeR in ##95, protection against parseInt("") = NaN
is now done through appending "|| 0" to the expression instead of
prepending "0" to the string
Merge pull request #96 from lucaswerkmeister/fix-95

Fix #95