Fix null pointer subtraction warning (#10498)
Fix null pointer subtraction warning (#10498)

The warning:
```
pqsort.c:106:7: warning: performing pointer subtraction with a null pointer has undefined behavior [-Wnull-pointer-subtraction]
loop:   SWAPINIT(a, es);
        ^~~~~~~~~~~~~~~
pqsort.c:65:47: note: expanded from macro 'SWAPINIT'
#define SWAPINIT(a, es) swaptype = ((char *)a - (char *)NULL) % sizeof(long) || \
```
Clang version:
```
Apple clang version 13.1.6 (clang-1316.0.21.2)
Target: x86_64-apple-darwin21.3.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
```
oranagra/redis,yossigo/redis,PKRoma/redis,neomantra/redis,soloestoy/redis,neomantra/redis,oranagra/redis,ofirluzon/redis,neomantra/redis,oranagra/redis,charsyam/redis,charsyam/redis,oranagra/redis,PKRoma/redis,yossigo/redis,oranagra/redis,PKRoma/redis,yossigo/redis,soloestoy/redis,ofirluzon/redis,PKRoma/redis,charsyam/redis,charsyam/redis,neomantra/redis,soloestoy/redis,yossigo/redis,ofirluzon/redis,ofirluzon/redis,soloestoy/redis,PKRoma/redis,yossigo/redis,neomantra/redis,soloestoy/redis,ofirluzon/redis,charsyam/redis