[Qt] Terminate string *pszExePath after readlink and without using memset

src/qt/guiutil.cpp

@@ -743,9 +743,10 @@ 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());