This fixes:

  hw/usb/dev-mtp.c:971:5: warning: 4th function call argument is an uninitialized value
      trace_usb_mtp_op_get_partial_object(s->dev.addr, o->handle, o->path,
                                           c->argv[1], c->argv[2]);
                                                       ^~~~~~~~~~
and:

  hw/usb/dev-mtp.c:981:12: warning: Assigned value is garbage or undefined
      offset = c->argv[1];
               ^ ~~~~~~~~~~

Reported-by: Clang Static Analyzer
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/usb/dev-mtp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c
index 560c61c7c1..b0ab6a7912 100644
--- a/hw/usb/dev-mtp.c
+++ b/hw/usb/dev-mtp.c
@@ -1017,12 +1017,16 @@ static MTPData *usb_mtp_get_object(MTPState *s, MTPControl *c,
 static MTPData *usb_mtp_get_partial_object(MTPState *s, MTPControl *c,
                                            MTPObject *o)
 {
-    MTPData *d = usb_mtp_data_alloc(c);
+    MTPData *d;
     off_t offset;
 
+    if (c->argc <= 2) {
+        return NULL;
+    }
     trace_usb_mtp_op_get_partial_object(s->dev.addr, o->handle, o->path,
                                         c->argv[1], c->argv[2]);
 
+    d = usb_mtp_data_alloc(c);
     d->fd = open(o->path, O_RDONLY);
     if (d->fd == -1) {
         usb_mtp_data_free(d);
-- 
2.17.1