Exit split if one of the split is empty

IllegalStateException is thrown if one of the splits is empty during
start animaiton. This CL performs the split dismiss action instead
of making the system-ui crash.

Bug: 273426456
Test: make a split with map app. start a full screen on top.
Change-Id: I5d2cae97187bb45df7b550cc99980c1aa792df2d