Makefile: added variable SCANBUILD

so that a different version of scan-build can be selected

lib/decompress/zstd_decompress.c

@@ -542,6 +542,7 @@ size_t ZSTD_getcBlockSize(const void* src, size_t srcSize,
 static size_t ZSTD_copyRawBlock(void* dst, size_t dstCapacity,
                           const void* src, size_t srcSize)
 {
+    if (dst==NULL) return ERROR(dstSize_tooSmall);
     if (srcSize > dstCapacity) return ERROR(dstSize_tooSmall);
     memcpy(dst, src, srcSize);
     return srcSize;

lib/legacy/zstd_v05.c

@@ -2846,6 +2846,7 @@ size_t ZSTDv05_getcBlockSize(const void* src, size_t srcSize, blockProperties_t*
 
 static size_t ZSTDv05_copyRawBlock(void* dst, size_t maxDstSize, const void* src, size_t srcSize)
 {
+    if (dst==NULL) return ERROR(dstSize_tooSmall);
     if (srcSize > maxDstSize) return ERROR(dstSize_tooSmall);
     memcpy(dst, src, srcSize);
     return srcSize;

lib/legacy/zstd_v06.c

@@ -3041,6 +3041,7 @@ size_t ZSTDv06_getcBlockSize(const void* src, size_t srcSize, blockProperties_t*
 
 static size_t ZSTDv06_copyRawBlock(void* dst, size_t dstCapacity, const void* src, size_t srcSize)
 {
+    if (dst==NULL) return ERROR(dstSize_tooSmall);
     if (srcSize > dstCapacity) return ERROR(dstSize_tooSmall);
     memcpy(dst, src, srcSize);
     return srcSize;