[gnome-boxes] installer-media: Don't use q35 with unknown OSes

[Felipe Borges <felipeborges src gnome org>]

commit f1af989c38efbf6b87a499fa65bb666dbf1c2883
Author: Fabiano Fidêncio <fabiano fidencio org>
Date:   Mon Dec 9 00:24:15 2019 +0100

    installer-media: Don't use q35 with unknown OSes
    
    Using q35 with unknown OSes is *too* error prone. Instead of doing
    so, let's fallback to "pc" type.
    
    https://gitlab.gnome.org/GNOME/gnome-boxes/issues/428
    
    Signed-off-by: Fabiano Fidêncio <fabiano fidencio org>

 src/installer-media.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/installer-media.vala b/src/installer-media.vala
index db3e2480..ef73668d 100644
--- a/src/installer-media.vala
+++ b/src/installer-media.vala
@@ -72,7 +72,7 @@
     public bool prefers_q35 {
         get {
             if (os == null)
-                return true;
+                return false;
 
             var device = find_device_by_prop (supported_devices, DEVICE_PROP_NAME, "qemu-x86-q35");
             if (device == null)