Don't free a shared buffer unless on iOS (strange but seems to be true)

internal/painter/gl/gl_gomobile.go

@@ -179,13 +179,6 @@ func (p *glPainter) glCreateBuffer(points []float32) Buffer {
 	return Buffer(sharedBuffer)
 }
 
-func (p *glPainter) glFreeBuffer(vbo Buffer) {
-	ctx := p.glctx()
-
-	ctx.BindBuffer(gl.ARRAY_BUFFER, gl.Buffer(vbo))
-	ctx.DeleteBuffer(gl.Buffer(vbo))
-}
-
 func (p *glPainter) glDrawTexture(texture Texture, alpha float32) {
 	ctx := p.glctx()
 	ctx.Enable(gl.BLEND)

internal/painter/gl/gl_gomobile_ios.go

@@ -0,0 +1,12 @@
+// +build ios
+
+package gl
+
+import "golang.org/x/mobile/gl"
+
+func (p *glPainter) glFreeBuffer(vbo Buffer) {
+	ctx := p.glctx()
+
+	ctx.BindBuffer(gl.ARRAY_BUFFER, gl.Buffer(vbo))
+	ctx.DeleteBuffer(gl.Buffer(vbo))
+}

internal/painter/gl/gl_gomobile_other.go

@@ -0,0 +1,7 @@
+// +build !ios
+
+package gl
+
+func (p *glPainter) glFreeBuffer(_ Buffer) {
+	// we don't free a shared buffer!
+}