check if fuzz input is graphical before decoding it to UTF8

fuzz/fuzz.rs

@@ -37,15 +37,15 @@ pub unsafe extern "C" fn LLVMFuzzerTestOneInput(input: *const u8, len: usize) ->
 
     let slice = unsafe { slice::from_raw_parts(input, len) };
 
+    if slice.iter().any(|b| !b.is_ascii_graphic()) {
+        return -1;
+    }
+
     let str = match str::from_utf8(slice) {
         Ok(str) => str,
         Err(_) => return -1,
     };
 
-    if !str.chars().all(|c| c.is_ascii_graphic()) {
-        return -1;
-    }
-
     let atom = str.trim();
 
     let mut stdin = PY_PROCESS.stdin.lock().expect("failed to get stdin lock");