fix strncpy() boundary condition (triggers GCC 9.x warning)

[karlthewex]

There are a few strncpy() invocations that could result in a string that is not NULL-terminated.

I see the warning using SPIFFS V0.3.7

Here's a git diff showing the suggested change that was applied locally.

diff --git a/source/third_party/spiffs/spiffs_hydrogen.c b/source/third_party/spiffs/spiffs_hydrogen.c
index 23c305a45..97a445f30 100644
--- a/source/third_party/spiffs/spiffs_hydrogen.c
+++ b/source/third_party/spiffs/spiffs_hydrogen.c
@@ -856,6 +856,7 @@ static s32_t spiffs_stat_pix(spiffs *fs, spiffs_page_ix pix, spiffs_file fh, spi
s->size = objix_hdr.size == SPIFFS_UNDEFINED_LEN ? 0 : objix_hdr.size;
s->pix = pix;
strncpy((char *)s->name, (char *)objix_hdr.name, SPIFFS_OBJ_NAME_LEN);

• s->name[SPIFFS_OBJ_NAME_LEN-1] = '\0'; // ensure string is NULL terminated
  #if SPIFFS_OBJ_META_LEN
  _SPIFFS_MEMCPY(s->meta, objix_hdr.meta, SPIFFS_OBJ_META_LEN);
  #endif
  diff --git a/source/third_party/spiffs/spiffs_nucleus.c b/source/third_party/spiffs/spiffs_nucleus.c
  index 6b052b0e3..88bd55cab 100644
  --- a/source/third_party/spiffs/spiffs_nucleus.c
  +++ b/source/third_party/spiffs/spiffs_nucleus.c
  @@ -945,6 +945,7 @@ s32_t spiffs_object_create(
  oix_hdr.type = type;
  oix_hdr.size = SPIFFS_UNDEFINED_LEN; // keep ones so we can update later without wasting this page
  strncpy((char*)oix_hdr.name, (const char*)name, SPIFFS_OBJ_NAME_LEN);
• oix_hdr.name[SPIFFS_OBJ_NAME_LEN-1] = '\0'; // ensure string is NULL terminated
  #if SPIFFS_OBJ_META_LEN
  if (meta) {
  _SPIFFS_MEMCPY(oix_hdr.meta, meta, SPIFFS_OBJ_META_LEN);
  @@ -1008,6 +1009,7 @@ s32_t spiffs_object_update_index_hdr(
  // change name
  if (name) {
  strncpy((char*)objix_hdr->name, (const char*)name, SPIFFS_OBJ_NAME_LEN);
• objix_hdr->name[SPIFFS_OBJ_NAME_LEN-1] = '\0'; // ensure string is NULL terminated
  }
  #if SPIFFS_OBJ_META_LEN
  if (meta) {