Added null checks before adding JSON elements to crash reports

[robert-smartbear]

Goal

Prevent rare issues from happening when a crash report is created while some data is not available (e.g. when Bugsnag is not fully initialized)

[github-actions[bot]]

	1 Error
:no_entry_sign:	Only release PRs should target the master branch

Bugsnag.framework binary size increased by 4,912 bytes from 713,264 to 718,176

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +1.9% +2.98Ki  +1.9% +2.98Ki    String Table
  +1.0% +2.30Ki  +1.0% +2.30Ki    __TEXT,__text
  +1.4% +1.75Ki  +1.4% +1.75Ki    Symbol Table
  +2.0%    +776  +2.0%    +776    __DATA,__objc_const
  +1.7%    +319  +1.7%    +319    __TEXT,__objc_methname
  +1.4%    +288  +1.4%    +288    __DATA,__cfstring
  +1.3%    +243  +1.3%    +243    __TEXT,__cstring
  +4.5%    +160  +4.5%    +160    __DATA,__objc_data
  +1.7%     +80  +1.7%     +80    __DATA,__objc_selrefs
  +5.5%     +59  +5.5%     +59    __TEXT,__objc_classname
  +1.8%     +36  +1.8%     +36    __TEXT,__objc_methtype
  +1.8%     +32  +1.8%     +32    Rebase Info
  +0.5%     +28  +0.5%     +28    [4 Others]
  +0.9%     +28  +0.9%     +28    __TEXT,__unwind_info
  [ = ]       0  +0.2%     +24    __DATA,__bss
  +0.6%     +16  +0.6%     +16    Binding Info
  +1.0%     +16  +1.0%     +16    Function Start Addresses
  +4.5%     +16  +4.5%     +16    __DATA,__objc_classlist
 -19.8% -1.32Ki -10.3% -1.34Ki    [__DATA]
 -16.0% -2.97Ki -16.0% -2.97Ki    [__TEXT]
  [ = ]       0 -64.4% -4.80Ki    [__LINKEDIT]
  +0.7% +4.80Ki  [ = ]       0    TOTAL

Generated by :no_entry_sign: Danger