Merge bitcoin#11193: [Qt] Terminate string *pszExePath after readlink…

… and without using memset

3a4401a [Qt] Terminate string *pszExePath after readlink and without using memset (practicalswift)

Pull request description:

  Terminate string `*pszExePath` after `readlink` and before passing to operator `<<`.

  * `ssize_t readlink(const char *pathname, char *buf, size_t bufsiz)` does not append a null byte to `buf`.
  * Operator `<<` expects a null-terminated string.

Tree-SHA512: fc18844bb23059fead8db0cb9b4b4ba6188f58e3f19ab4719c2737cc5dd6df23ae7d4804ef2820d39b334204a48ee3de1d202c272bcd156e60761af2fcb9349d

src/qt/guiutil.cpp

@@ -814,9 +814,10 @@ bool SetStartOnSystemStartup(bool fAutoStart)
     else
     {
         char pszExePath[MAX_PATH+1];
-        memset(pszExePath, 0, sizeof(pszExePath));
-        if (readlink("/proc/self/exe", pszExePath, sizeof(pszExePath)-1) == -1)
+        ssize_t r = readlink("/proc/self/exe", pszExePath, sizeof(pszExePath) - 1);
+        if (r == -1)
             return false;
+        pszExePath[r] = '\0';
 
         fs::create_directories(GetAutostartDir());