[client] X11: release pointer after capture

Normal input now uses absolute positioning, so retaining the XI pointer
grab after capture leaves no later path to release it.

Always release the grab so leaving the window works again and the
uncapture path can align the host cursor to the guest position.

client/tests/mouse_test.c

@@ -67,6 +67,7 @@ static struct
   struct Trap           conf;
   struct Trap           lock;
   bool                  valid;
+  bool                  captureGrab;
   struct Ev             ev[256];
   unsigned int          count;
 }
@@ -152,6 +153,18 @@ static void capture(void)
     return;
   }
 
+  if (m.captureGrab)
+  {
+    m.conf.req = true;
+    if (!m.conf.hold)
+      m.conf.on = true;
+    m.lock.req = true;
+    if (!m.lock.hold)
+      m.lock.on = m.conf.on;
+    push(EV_CAPTURE, 0, 0, false);
+    return;
+  }
+
   m.conf.req = false;
   if (!m.conf.hold)
     m.conf.on = false;
@@ -171,6 +184,9 @@ static void uncapture(void)
   m.lock.req = false;
   if (!m.lock.hold)
     m.lock.on = false;
+
+  if (m.captureGrab)
+    ungrab();
 }
 
 static bool captured(void)
@@ -592,6 +608,38 @@ static void testCapAlign(void)
   CHECK(!m.ev[warp].exit);
 }
 
+static void testX11CapExit(void)
+{
+  reset();
+  setLocal(50, 50);
+  m.support     = LG_DS_WARP_SCREEN;
+  m.captureGrab = true;
+  m.conf.req    = false;
+  m.conf.on     = false;
+
+  core_setGrabQuiet(true);
+  CHECK(m.conf.on);
+  CHECK(m.lock.on);
+
+  g_cursor.guest.x += 10;
+  m.count = 0;
+  core_setGrabQuiet(false);
+
+  const int uncapture = first(EV_UNCAPTURE);
+  const int ungrab    = first(EV_UNGRAB);
+  const int warp      = first(EV_WARP);
+  CHECK(uncapture >= 0);
+  CHECK(ungrab > uncapture);
+  CHECK(warp > ungrab);
+  CHECK(m.ev[warp].x == 60);
+  CHECK(m.ev[warp].y == 50);
+  CHECK(!m.ev[warp].exit);
+  CHECK(!m.conf.req);
+  CHECK(!m.conf.on);
+  CHECK(!m.lock.req);
+  CHECK(!m.lock.on);
+}
+
 static void testCapFallback(void)
 {
   reset();
@@ -853,6 +901,7 @@ static const struct Test tests[] = {
   { "capture-revoked" , testCapRevoke    },
   { "capture-release" , testCapRelease   },
   { "capture-align"   , testCapAlign     },
+  { "x11-capture-exit", testX11CapExit   },
   { "capture-fallback", testCapFallback  },
   { "rotate-scale"    , testRotateScale  },
   { "geometry"        , testGeometry     },