app: add iPad Mini 3, and a fallback PPI

Change-Id: I46cde56fe7f9a13de71bbb8c80b81cd273dd020f
Reviewed-on: https://go-review.googlesource.com/10540
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/app/darwin_armx.go b/app/darwin_armx.go
index c3b238a..f973fc2 100644
--- a/app/darwin_armx.go
+++ b/app/darwin_armx.go
@@ -86,6 +86,8 @@
 	"iPad4,3":   264, // iPad Air LTE China
 	"iPad4,4":   326, // iPad Mini gen2 wifi
 	"iPad4,5":   326, // iPad Mini gen2 LTE
+	"iPad4,6":   326, // iPad Mini 3
+	"iPad4,7":   326, // iPad Mini 3
 	"iPhone3,1": 326, // iPhone 4
 	"iPhone4,1": 326, // iPhone 4S
 	"iPhone5,1": 326, // iPhone 5
@@ -103,7 +105,8 @@
 	name := C.GoString(&C.sysInfo.machine[0])
 	v, ok := machinePPI[name]
 	if !ok {
-		log.Fatalf("unknown machine: %s", name)
+		log.Printf("unknown machine: %s", name)
+		v = 163 // emergency fallback
 	}
 	return v
 }