Fix bare except clauses in httpbin/core.py and httpbin/helpers.py

[koteshyelamati]

Replace 4 bare except: clauses with specific exception types across two files.

httpbin/core.py (2 fixes → except Exception:):

• Bugsnag initialization fallback
• Base64 URL-safe decode error handler

httpbin/helpers.py (2 fixes → except (ValueError, IndexError):):

• Two int() parse attempts in the byte-range header parser

Bare except: catches BaseException including SystemExit and KeyboardInterrupt, which is almost never intended. Specific exception types make the error handling explicit and safe.