Null-terminate buffers that strncpy writes to (#24095)

It is possible that the string being copied is so large that strncpy
fills up the destination array and does not write any null characters to
it. That will lead to buffer overflows. Work around that by always
writing a null character at the end of the destination array.

Author: omajid

src/corefx/System.Globalization.Native/pal_calendarData.c

@@ -305,6 +305,8 @@ static int32_t EnumSymbols(const char* locale,
 
     char localeWithCalendarName[ULOC_FULLNAME_CAPACITY];
     strncpy(localeWithCalendarName, locale, ULOC_FULLNAME_CAPACITY);
+    localeWithCalendarName[ULOC_FULLNAME_CAPACITY - 1] = 0;
+
     uloc_setKeywordValue("calendar", GetCalendarName(calendarId), localeWithCalendarName, ULOC_FULLNAME_CAPACITY, &err);
 
     UCalendar* pCalendar = ucal_open(NULL, 0, localeWithCalendarName, UCAL_DEFAULT, &err);
@@ -412,6 +414,7 @@ static int32_t EnumAbbrevEraNames(const char* locale,
     char* parentNamePtr = parentNameBuf;
 
     strncpy(localeNamePtr, locale, ULOC_FULLNAME_CAPACITY);
+    localeNamePtr[ULOC_FULLNAME_CAPACITY - 1] = 0;
 
     while (TRUE)
     {