Fix #1533 (#1534)

Author: feliam

manticore/ethereum/solidity.py

@@ -109,7 +109,7 @@ def __build_source_map(self, bytecode, srcmap):
         # https://solidity.readthedocs.io/en/develop/miscellaneous.html#source-mappings
         new_srcmap = {}
         bytecode = self._without_metadata(bytecode)
-        if self.source_code and srcmap:
+        if self.source_code and bytecode and srcmap:
 
             asm_offset = 0
             asm_pos = 0