don't fail hard on zero tvl

[joe-bowman]

• in a situation where we have been unable to obtain TVLs for any zones (i.e. connection to osmosis is down at the epoch boundary), we shouldn't cause the epoch hook to fail and roll back, but be okay with a zero allocation this epoch.

This is unlikely to happen in production, but not having it means that if this situation does arise the following epoch will also be affected due to not resetting the epoch boundary heights for each zone.

[codecov-commenter]

Codecov Report

Merging #532 (4491a69) into develop (349addf) will decrease coverage by 0.02%.
Report is 2 commits behind head on develop.
The diff coverage is 23.07%.

@@             Coverage Diff             @@
##           develop     #532      +/-   ##
===========================================
- Coverage    53.62%   53.60%   -0.02%     
===========================================
  Files          186      186              
  Lines        14639    14650      +11     
===========================================
+ Hits          7850     7853       +3     
- Misses        6131     6138       +7     
- Partials       658      659       +1     

Flag	Coverage Δ
unittests	53.60% <23.07%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
x/participationrewards/keeper/hooks.go	53.68% <0.00%> (ø)
x/interchainstaking/keeper/hooks.go	71.16% <11.11%> (-3.51%)	⬇️
x/interchainstaking/keeper/redelegation_record.go	90.90% <100.00%> (+0.34%)	⬆️