[core] don't access empty texture pos optionals when buckets are out of sync

src/mbgl/renderer/layers/render_line_layer.cpp

@@ -143,8 +143,8 @@ void RenderLineLayer::render(PaintParameters& parameters, RenderSource*) {
                      texsize,
                      crossfade,
                      parameters.pixelRatio),
-                     *posA,
-                     *posB,
+                     posA,
+                     posB,
                      LinePatternProgram::TextureBindings{
                          textures::image::Value{ *geometryTile.iconAtlasTexture->resource, gfx::TextureFilterType::Linear },
                      });

src/mbgl/renderer/paint_property_binder.hpp

@@ -148,7 +148,7 @@ public:
     void upload(gfx::Context&) override {}
 
     void setPatternParameters(const optional<ImagePosition>& posA, const optional<ImagePosition>& posB, CrossfadeParameters&) override {
-        if (!posA && !posB) {
+        if (!posA || !posB) {
             return;
         } else {
             constantPatternPositions = std::tuple<std::array<uint16_t, 4>, std::array<uint16_t, 4>> { posB->tlbr(), posA->tlbr() };