Add nicer "non-existent file path" error #90
Description
Currently if you pass a file path that's non-existent you get this.
➜ nat-api git:(master) ✗ ./node_modules/.bin/tsup lib/index.ts --format esm,cjs,iife --dts
CLI Target: es2018
ESM Build start
CJS Build start
IIFE Build start
IIFE Build success in 22ms
ESM Build success in 77ms
CJS Build success in 76ms
DTS Build start
Error: You must supply options.input to rollup
at Graph.generateModuleGraph (/Users/xo/code/OmgImAlexis/nat-api/node_modules/rollup/dist/shared/rollup.js:18433:19)
at async Graph.build (/Users/xo/code/OmgImAlexis/nat-api/node_modules/rollup/dist/shared/rollup.js:18397:9)
at async rollupInternal (/Users/xo/code/OmgImAlexis/nat-api/node_modules/rollup/dist/shared/rollup.js:19370:9)
at async runRollup (/Users/xo/code/OmgImAlexis/nat-api/node_modules/tsup/dist/rollup.js:1427:20)
at async MessagePort.<anonymous> (/Users/xo/code/OmgImAlexis/nat-api/node_modules/tsup/dist/rollup.js:1463:5)