[Placeholder] Frontend bugs

[aaronxsu]

WIP...

1. in client/api.ts: handling of undefined when .catch(error => reject(error.response.data));: https://rollbar.com/Azavea/DistrictBuilder/items/138/
2. in client/components/map/index.ts: districtsDefinition might be empty: https://rollbar.com/Azavea/DistrictBuilder/items/171/

File client/components/map/index.ts:658:27 in lE
districtsDefinition.some(districtId =>
File client/components/map/index.ts:649:7 in lE
? isGeoUnitLocked(
File client/components/map/index.ts:649:7 in lE
? isGeoUnitLocked(
File client/components/map/index.ts:846:11 in [anonymous]
if (isGeoUnitLocked(districtsDefinition, lockedDistricts, geoUnitIndices)) {
File client/components/map/index.ts:844:22 in [anonymous]
geoUnitsForLevel.forEach((geoUnitIndices, featureId) => {
File client/components/map/index.ts:843:28 in yE
Object.entries(geoUnits).forEach(([geoLevel, geoUnitsForLevel]) => {
File client/components/map/index.ts:823:3 in mE
removeLockedGeoUnits(
File client/components/map/index.ts:882:10 in gE
return onlyUnlockedGeoUnits(