Update 0051-n-queens.c

[BugIdentifier]

This is a bug fix for an existing solution. The problem is that x is not defined in the for loop. Hence, for loop will fail to be executed

• File(s) Modified: 0051-n-queens.c
• Language(s) Used: c
• Submission URL: https://leetcode.com/submissions/detail/1299108287/

Important

Please make sure the file name is lowercase and a duplicate file does not already exist before merging.

[Ykhan799]

@BugIdentifier Thank you for your fix 👍