Meta: Only enable the SPICE server when using the SPICE display

Newer versions of QEMU prevent the user from running a GL-rendered
display while a SPICE display is active due to incompatibilities.

Since there is no way to disable QEMUs (apparently implicit) SPICE
display, make sure that we only enable SPICE support if the user
requested running with SPICE specifically. In this case, QEMU picks the
default SPICE client instead of rendering a display using whatever our
default on that platform would be.

Meta/run.sh

@@ -351,7 +351,7 @@ $SERENITY_SPICE_SERVER_CHARDEV
 "
 
 if [ "$SERENITY_ARCH" != "aarch64" ]; then
-    if "${SERENITY_QEMU_BIN}" -chardev help | grep -iq spice; then
+    if [ "${SERENITY_SPICE}" ] && "${SERENITY_QEMU_BIN}" -chardev help | grep -iq spice; then
         SERENITY_COMMON_QEMU_ARGS="$SERENITY_COMMON_QEMU_ARGS
         -spice port=5930,agent-mouse=off,disable-ticketing=on
         "