OSV-2020-1023 Use-of-uninitialized-value in njs_vsprintf

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=23061 Crash type: Use-of-uninitialized-value Crash state: njsvsprintf njserrorfmtnew njsregexpmatchtracehandler...