q-dev: fix hex characters validation

Using "i" as a loop iterator conflicts with the outer loop, effectively
turning it into infinite loop.
Use a generator instead.

qubesusbproxy/core3ext.py

@@ -299,9 +299,9 @@ def _sanitize(
                         break
                     hex_code = untrusted_device_desc[i - 1: i + 1]
                     try:
-                        for i in range(2):
-                            if hex_code[i] not in b'0123456789abcdefABCDEF':
-                                raise ValueError()
+                        if any(h not in b'0123456789abcdefABCDEF'
+                               for h in hex_code):
+                            raise ValueError()
                         hex_value = int(hex_code, 16)
                         c = chr(hex_value)
                     except ValueError: