Fixing bugs found by static analysis

api/index.php

classes/api.php

classes/article.php

classes/auth/base.php

classes/db/pdo.php

classes/handler/public.php

classes/pluginhost.php

classes/pref/filters.php

classes/pref/prefs.php

classes/rpc.php

classes/ttrssmailer.php

include/colors.php

include/functions.php

include/rssfuncs.php

index.php

install/index.php

lib/MiniTemplator.class.php

lib/phpqrcode/bindings/tcpdf/qrcode.php

lib/phpqrcode/phpqrcode.php

lib/phpqrcode/qrencode.php