filter non elf files from make_sql_engine

We should filter non elf files from make_sql_engine otherwise the
NoneType gets passed down to the generators.

* added unit test

sqlelf/sql.py

@@ -63,7 +63,9 @@ def make_sql_engine(filenames: list[str], recursive: bool = False) -> SQLEngine:
         recursive: whether to recursively load all shared
                 libraries needed by each binary
     """
-    binaries: list[lief.Binary] = [lief.parse(filename) for filename in filenames]
+    binaries: list[lief.Binary] = [
+        lief.parse(filename) for filename in filenames if lief.is_elf(filename)
+    ]
     connection = apsw.Connection(":memory:")
 
     if recursive:

tests/test_sql.py

@@ -66,3 +66,9 @@ def test_select_zero_rows() -> None:
     engine = sql.make_sql_engine(["/bin/ls"])
     result = list(engine.execute("SELECT * FROM elf_headers LIMIT 0"))
     assert len(result) == 0
+
+
+def test_non_existent_file() -> None:
+    engine = sql.make_sql_engine(["/doesnotexist"])
+    result = list(engine.execute("SELECT * FROM elf_headers LIMIT 1"))
+    assert len(result) == 0