gl1/gl2/gl3: an overlay page's last image is in bounds, and name 0 is not art

The overlay id check read `image > gl->overlays`, one past the page's
last entry, and the tex_geom setters had no check at all - a write
through a NULL coordinate array before a page is loaded, or into the
neighbouring region of the block the three coordinate arrays share.

gl3_render_overlay() also drew entries whose texture name was 0. That
is black on a core context, but a GLES driver may sample whatever the
unit last held, which on the alpha blend pipeline's unit is the
content texture - the page's art then shows the core image.

gfx/drivers/gl1.c

@@ -1254,10 +1254,10 @@ static void gl1_overlay_vertex_geom(void *data,
    GLfloat *vertex = NULL;
    gl1_t *gl        = (gl1_t*)data;
 
-   if (!gl)
+   if (!gl || !gl->overlay_vertex_coord)
       return;
 
-   if (image > gl->overlays)
+   if (image >= gl->overlays)
    {
       RARCH_ERR("[GL1] Invalid overlay id: %u.\n", image);
       return;
@@ -1287,7 +1287,10 @@ static void gl1_overlay_tex_geom(void *data,
    GLfloat *tex = NULL;
    gl1_t *gl     = (gl1_t*)data;
 
-   if (!gl)
+   if (!gl || !gl->overlay_tex_coord)
+      return;
+
+   if (image >= gl->overlays)
       return;
 
    tex          = (GLfloat*)&gl->overlay_tex_coord[image * 8];

gfx/drivers/gl2.c

@@ -2993,10 +2993,10 @@ static void gl2_overlay_vertex_geom(void *data,
    GLfloat *vertex = NULL;
    gl2_t *gl       = (gl2_t*)data;
 
-   if (!gl)
+   if (!gl || !gl->overlay_vertex_coord)
       return;
 
-   if (image > gl->overlays)
+   if (image >= gl->overlays)
    {
       RARCH_ERR("[GL] Invalid overlay id: %u\n", image);
       return;
@@ -3026,7 +3026,10 @@ static void gl2_overlay_tex_geom(void *data,
    GLfloat *tex = NULL;
    gl2_t *gl    = (gl2_t*)data;
 
-   if (!gl)
+   if (!gl || !gl->overlay_tex_coord)
+      return;
+
+   if (image >= gl->overlays)
       return;
 
    tex          = (GLfloat*)&gl->overlay_tex_coord[image * 8];

gfx/drivers/gl3.c

@@ -1830,10 +1830,10 @@ static void gl3_overlay_vertex_geom(void *data,
    GLfloat *vertex = NULL;
    gl3_t       *gl = (gl3_t*)data;
 
-   if (!gl)
+   if (!gl || !gl->overlay_vertex_coord)
       return;
 
-   if (image > gl->overlays)
+   if (image >= gl->overlays)
       return;
 
    vertex          = (GLfloat*)&gl->overlay_vertex_coord[image * 8];
@@ -1860,7 +1860,10 @@ static void gl3_overlay_tex_geom(void *data,
    GLfloat *tex = NULL;
    gl3_t *gl    = (gl3_t*)data;
 
-   if (!gl)
+   if (!gl || !gl->overlay_tex_coord)
+      return;
+
+   if (image >= gl->overlays)
       return;
 
    tex          = (GLfloat*)&gl->overlay_tex_coord[image * 8];
@@ -1880,6 +1883,9 @@ static void gl3_render_overlay(gl3_t *gl,
 {
    size_t i;
 
+   if (!gl->overlay_tex || !gl->overlays)
+      return;
+
    glEnable(GL_BLEND);
    glDisable(GL_CULL_FACE);
    glDisable(GL_DEPTH_TEST);
@@ -1915,6 +1921,10 @@ static void gl3_render_overlay(gl3_t *gl,
 
    for (i = 0; i < gl->overlays; i++)
    {
+      /* Name 0 is black only on a core context; a GLES driver may
+       * sample whatever the unit last held. */
+      if (!gl->overlay_tex[i])
+         continue;
       glActiveTexture(GL_TEXTURE1);
       glBindTexture(GL_TEXTURE_2D, gl->overlay_tex[i]);
       glDrawArrays(GL_TRIANGLE_STRIP, (GLint)(4 * i), 4);