SEGV in redisvFormatCommand

[cherry530]

An access wild address issue occurred while testing with fuzz.
The specific logs are as follows:
==2229501==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000201 (pc 0x7faebd07c8c1 bp 0x7fffd934d9d0 sp 0x7fffd934d188 T0)
==2229501==The signal is caused by a READ memory access.
==2229501==Hint: address points to the zero page.
#0 0x7faebd07c8c1 (/lib64/libc.so.6+0x15b8c1)
#1 0x4b7a98 in strlen /src/llvm-project/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc
#2 0x552086 in redisvFormatCommand /src/hiredis/hiredis.c:357:24
#3 0x55373e in redisFormatCommand /src/hiredis/hiredis.c:554:11
#4 0x551379 in LLVMFuzzerTestOneInput /src/hiredis/format_command_fuzzer.c:51:5
#5 0x459ae3 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:599:15
#6 0x445252 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:323:6
#7 0x44aef6 in fuzzer::FuzzerDriver(int*, char***, int ()(unsigned char const, unsigned long)) /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:856:9
#8 0x474402 in main /src/llvm-project/compiler-rt/lib/fuzzer/FuzzerMain.cpp:20:10
#9 0x7faebcf46b26 in __libc_start_main (/lib64/libc.so.6+0x25b26)
#10 0x421109 in _start (/root/oss-fuzz/build/out/hiredis/format_command_fuzzer+0x421109)

DEDUP_TOKEN: strlen--redisvFormatCommand
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib64/libc.so.6+0x15b8c1)
==2229501==ABORTING

[cherry530]

See the following code that the log identifies as int redisvFormatCommand(char *target, const char format, va_list ap)
case 's':
arg = va_arg(ap,char);
size = strlen(arg);
if (size > 0)
newarg = sdscatlen(curarg,arg,size);
break;
va_arg(ap,char): an invalid address was returned,please check

[cherry530]

@pietern Please check and deal with it