Fix some warnings in qtquick1 found by Clang

qml/qdeclarativevme.cpp:286:26: error: destination for this 'memset' call is a pointer to dynamic class 'QObject'; vtable pointer will be overwritten [-Werror,-Wdynamic-class-memaccess]
qml/qdeclarativemetatype.cpp:441:9: error: expression result unused; should this cast be to 'void'? [-Werror,-Wunused-value]
util/qdeclarativefontloader.cpp:87:52: error: addition of default argument on redeclaration makes this constructor a default constructor [-Werror,-Wdefault-arg-special-member]

Cherry-picked from qtquick1/99f138ad08101315cc871489c78cd10755b046b0

Change-Id: If0a690eacf9421f932214d2917cd3fa0a7daac9a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
QHttpMultipart: reset read pointer when device is reset

... otherwise we would not read from the beginning when trying to
read again. The device is reset when we try to resend a request
(e.g. remote host closed etc.).

(cherry picked from commit 795468bdc68931a90454bd1c975f7de7ba670e3b)

Change-Id: I8d7b3afb64b9cd25ee7c13b78f0b470d9dae3021
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>
QNonContiguousByteDevice: reset() instead of seek() if possible

... because e.g. QHttpMultiPartIODevice does not implement seek at all
(QTBUG-30295), which would make resetting such a device fail.

(cherry picked from commit 804a067846cd90e3ca31f985d539c8d75d654d82)

Change-Id: I8ba1ef76cc6e7f5ebf0b39c9a75e3aea26980b82
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>