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.

Closes #8648