Make TextSelectionSizer a bit easier to understand standalone

Nothing really changes because it's only used in one place and that
place called getRegion so there's no leak but looking at the class
standalone one could think that one would get a leak if getRegion was
not called.
7 jobs for TextSelectionSizer in 5 minutes and 22 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #7621091
build

00:05:22

passed #7621096
build_android

00:01:03

passed #7621092
build_clang_libcpp

00:05:03

passed #7621095
build_clazy

00:04:01

passed #7621094
build_mingw64_fedora

00:02:30

passed #7621093
build_ubuntu_16_04

00:02:31

passed #7621090
clang_format

00:01:18