fix: ensure hardhat does not fail if no input sources provided (#688)

* fix: ensure hardhat does not fail if no input sources provided

* lint: fix

* chore: add changeset
Co-authored-by: smartcontracts <kelvinfichter@gmail.com>
Co-authored-by: Georgios Konstantopoulos <me@gakonst.com>

.changeset/olive-fishes-share.md

+---
+'@eth-optimism/hardhat-ovm': patch
+---
+
+Ensure hardhat does not fail if no input sources provided

packages/hardhat-ovm/src/index.ts

@@ -161,6 +161,8 @@ subtask(
       }
     }
 
+    if (Object.keys(ovmInput.sources).length === 0) return {}
+
     // Build both inputs separately.
     const ovmOutput = await hre.run(TASK_COMPILE_SOLIDITY_RUN_SOLCJS, {
       input: ovmInput,