assume no unicode if no source code is available

slither/core/source_mapping/source_mapping.py

@@ -150,9 +150,10 @@ def _compute_line(
     return list(range(start_line, end_line + 1)), starting_column, ending_column
 
 
+# pylint: disable=too-many-locals
 def _convert_source_mapping(
     offset: str, compilation_unit: "SlitherCompilationUnit"
-) -> Source:  # pylint: disable=too-many-locals
+) -> Source:
     """
     Convert a text offset to a real offset
     see https://solidity.readthedocs.io/en/develop/miscellaneous.html#source-mappings
@@ -186,11 +187,15 @@ def _convert_source_mapping(
     filename: Filename = compilation_unit.core.crytic_compile.filename_lookup(filename_used)
     is_dependency = compilation_unit.core.crytic_compile.is_dependency(filename.absolute)
 
-    # convert byte-offset indicies to char-offset
-    source_code = compilation_unit.core.source_code[filename.absolute]
-    s = int(len(source_code.encode("utf-8")[:s_bytes].decode("utf-8")))
-    l = int(len(source_code.encode("utf-8")[s_bytes : s_bytes + l_bytes].decode("utf-8")))
-    f = int(f)
+    if filename.absolute in compilation_unit.core.source_code:
+        # convert byte-offset indicies to char-offset
+        source_code = compilation_unit.core.source_code[filename.absolute]
+        s = int(len(source_code.encode("utf-8")[:s_bytes].decode("utf-8")))
+        l = int(len(source_code.encode("utf-8")[s_bytes : s_bytes + l_bytes].decode("utf-8")))
+    else:
+        # no source code is available, hopefully the source code doesn't contain unicode
+        s = int(s_bytes)
+        l = int(l_bytes)
 
     (lines, starting_column, ending_column) = _compute_line(compilation_unit, filename, s, l)