[BugFix] fix BE crash during startup when its started from deep nested directory path (backport #51075)

[mergify]

Why I'm doing:

BE crash during startup when its started from deep nested directory path

What I'm doing:

max field width should be specified in fscanf() so that it does not overflow the buffer

I20240918 01:53:30.107084 135614079983936 starrocks_be.cpp:264] BE start step 10: start brpc server successfully
I20240918 01:53:30.108626 135614079983936 starrocks_be.cpp:273] BE start step 11: start http server successfully
I20240918 01:53:30.108730 135614079983936 thrift_server.cpp:384] heartbeat has started listening port on 9050
I20240918 01:53:30.108733 135614079983936 starrocks_be.cpp:291] BE start step 12: start heartbeat server successfully
I20240918 01:53:30.108734 135614079983936 starrocks_be.cpp:293] BE started successfully

Fixes #51074

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.3
  • 3.2
  • 3.1
  • 3.0
  • 2.5

---

This is an automatic backport of pull request #51075 done by [Mergify](https://mergify.com). ## Why I'm doing: BE crash during startup when its started from deep nested directory path

What I'm doing:

max field width should be specified in fscanf() so that it does not overflow the buffer

I20240918 01:53:30.107084 135614079983936 starrocks_be.cpp:264] BE start step 10: start brpc server successfully
I20240918 01:53:30.108626 135614079983936 starrocks_be.cpp:273] BE start step 11: start http server successfully
I20240918 01:53:30.108730 135614079983936 thrift_server.cpp:384] heartbeat has started listening port on 9050
I20240918 01:53:30.108733 135614079983936 starrocks_be.cpp:291] BE start step 12: start heartbeat server successfully
I20240918 01:53:30.108734 135614079983936 starrocks_be.cpp:293] BE started successfully

Fixes #51074

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr