fix [2931718] glDrawArrays skips a triangle when more than 70 vertices are used.

a typo prevented the last 2 vertices of a batch to be copied to the front of
the next batch. Instead, the 2 very first vertices were used.

Change-Id: I3c344784dac1cef64df2fb6f6efb2f901cc788db
diff --git a/opengl/libagl/array.cpp b/opengl/libagl/array.cpp
index 4997dc8..7fbe9b5 100644
--- a/opengl/libagl/array.cpp
+++ b/opengl/libagl/array.cpp
@@ -685,8 +685,8 @@
             } while (num);
         }
         if (count) {
-            v0 = c->vc.vBuffer + 2 + num - 2;
-            v1 = c->vc.vBuffer + 2 + num - 1;
+            v0 = c->vc.vBuffer + 2 + vcs - 2;
+            v1 = c->vc.vBuffer + 2 + vcs - 1;
             if ((winding&2) == 0) {
                 // for strips copy back the two last compiled vertices
                 c->vc.vBuffer[0] = *v0;