TipNode: fix bug in selecting multi-finger tip

Finger size is a formatted string that must be cast as a
float before comparison to the robot tip diameter.

BUG=b:148627899
TEST=Run test with multi-finger tip. Test runs without error.

Change-Id: I53c38ce6f44ef94c32d871500fe142105f1bd409
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/optofidelity_TPPT/+/2425122
Reviewed-by: Harry Cutts <hcutts@chromium.org>
Commit-Queue: Sean O'Brien <seobrien@chromium.org>
Tested-by: Sean O'Brien <seobrien@chromium.org>
1 file changed