IO: fix an off-by-one bug

src/common/io/io_unix.c

@@ -29,7 +29,7 @@ static void createSubfolders(const char* fileName)
     while((token = strchr(fileName, '/')) != NULL)
     {
         uint32_t length = (uint32_t)(token - fileName + 1);
-        pathTail = ffStrCopyN(pathTail, fileName, length);
+        pathTail = ffStrCopyN(pathTail, fileName, length + 1);
         mkdir(path, S_IRWXU | S_IRGRP | S_IROTH);
         fileName = token + 1;
     }

src/common/io/io_windows.c

@@ -14,7 +14,7 @@ static void createSubfolders(const char* fileName)
     while((token = strchr(fileName, '/')) != NULL)
     {
         uint32_t length = (uint32_t)(token - fileName + 1);
-        pathTail = ffStrCopyN(pathTail, fileName, length);
+        pathTail = ffStrCopyN(pathTail, fileName, length + 1);
         CreateDirectoryA(path, NULL);
         fileName = token + 1;
     }

src/util/stringUtils.h

@@ -80,6 +80,7 @@ static inline bool ffCharIsDigit(char c)
     return '0' <= c && c <= '9';
 }
 
+// ffStrCopyN copies at most (nDst - 1) bytes from src to dst
 static inline char* ffStrCopyN(char* __restrict__ dst, const char* __restrict__ src, size_t nDst)
 {
     assert(dst != NULL);