Added missing check for array key in `GelfMessageFormatter`
Added missing check for array key in `GelfMessageFormatter`

yegortokmakov/monolog,Seldaek/monolog,thiagotalma/monolog,localheinz/monolog,JCook21/monolog,pomaxa/monolog,oswaldderiemaecker/monolog,JeroenDeDauw/monolog,0x46616c6b/monolog,rap2hpoutre/monolog,cherrytech/monolog,Sgoettschkes/monolog,dangnguyen27/monolog,tavrij/test,prgTW/monolog,lyrixx/monolog,netgusto/monolog,webwlsong/monolog,supre/monolog,aeryaguzov/monolog,mbrevda/monolog,brendo/monolog,printerpam/monolog,esalter/monolog,chinaweilu/monolog,dailymotion/monolog,gencer/monolog,bd808/monolog,deguif/monolog,yaoshanliang/monolog,dracony/monolog,KevinMGranger/monolog,entwu/monolog