[core] set u_texture uniform value

fix #1685

src/mbgl/renderer/painter_symbol.cpp

@@ -54,6 +54,7 @@ void Painter::renderSDF(SymbolBucket &bucket,
     sdfShader.u_exmatrix = exMatrix;
     sdfShader.u_texsize = texsize;
     sdfShader.u_skewed = skewed;
+    sdfShader.u_texture = 0;
 
     // adjust min/max zooms for variable font sies
     float zoomAdjust = std::log(fontSize / bucketProperties.size) / std::log(2);
@@ -232,6 +233,7 @@ void Painter::renderSymbol(SymbolBucket& bucket, const SymbolLayer& layer, const
             iconShader->u_texsize = {{ float(spriteAtlas->getWidth()) / 4.0f, float(spriteAtlas->getHeight()) / 4.0f }};
             iconShader->u_skewed = skewed;
             iconShader->u_extra = extra;
+            iconShader->u_texture = 0;
 
             // adjust min/max zooms for variable font sies
             float zoomAdjust = std::log(fontSize / layout.icon.size) / std::log(2);

src/mbgl/shader/icon_shader.hpp

@@ -23,6 +23,7 @@ public:
     Uniform<std::array<GLfloat, 2>> u_texsize     = {"u_texsize",     *this};
     Uniform<GLint>                  u_skewed      = {"u_skewed",      *this};
     Uniform<GLfloat>                u_extra       = {"u_extra",       *this};
+    Uniform<GLint>                  u_texture     = {"u_texture",     *this};
 
 protected:
     GLint a_offset = -1;

src/mbgl/shader/sdf_shader.hpp

@@ -22,6 +22,7 @@ public:
     Uniform<GLfloat>                u_maxfadezoom = {"u_maxfadezoom", *this};
     Uniform<GLfloat>                u_fadezoom    = {"u_fadezoom",    *this};
     Uniform<GLint>                  u_skewed      = {"u_skewed",      *this};
+    Uniform<GLint>                  u_texture     = {"u_texture",     *this};
 
 protected:
     GLint a_offset = -1;