[map] Fix equality

Ouch!

src/hb-map.hh

@@ -258,7 +258,7 @@ struct hb_hashmap_t
     if (population != other.population) return false;
 
     for (auto pair : iter ())
-      if (get (pair.first) != pair.second)
+      if (other.get (pair.first) != pair.second)
         return false;
 
     return true;

src/test-map.cc

@@ -249,6 +249,16 @@ main (int argc, char **argv)
     m.set (1, bytes);
     assert (m.has (1));
   }
+  /* Test equality. */
+  {
+    hb_map_t m1, m2, m3;
+    m1.set (1, 2);
+    m2.set (1, 2);
+    m3.set (1, 3);
+    assert (m1 == m2);
+    assert (m1 != m3);
+    assert (!(m2 == m3));
+  }
 
   return 0;
 }