split-select: fix OSX build

Clang is a bit stricter about what template definition it chooses
for mixed types that are normally possible to cast between.
Operations like std::find(int iterator, int iterator, enum) will fail,
as Clang won't implicitly cast an enum to an int here.

Change-Id: Ib2276c382ebf2b877e1045d32b1a9d0a1fa4d4a4