perf(jqLite): only take str.split() path when needed

bda673f8e785f299407c8c45887f37448a0f0192 changed code to only use
`str.split()` when necessary, but the result was that `str.split()` would
always be taken unless ' ' was the first character in the string, negating the
effectiveness of the perf fix.

/cc @IgorMinar --- re https://github.com/angular/angular.js/commit/bda673f8e785f299407c8c45887f37448a0f0192#commitcomment-7417474

Lets check this in fast, since it's such a tiny change