Fixed a crash on reportNetworkRequestSpan

[robert-smartbear]

Goal

Prevent a crash when User calls reportNetworkRequestSpan without setting networkRequestCallback on BugsnagPerformanceConfiguration

Changeset

Added a safeguard preventing a null being assigned to networkRequestCallback_ in BugsnagPerformanceImpl class

Testing

E2E tests

[github-actions]

BugsnagPerformance.framework binary size did not change - 459,640 bytes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +24  +0.0%     +24    __TEXT,__text
  -0.1%     -24  -0.1%     -24    [__TEXT]
  [ = ]       0  [ = ]       0    TOTAL

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