Fix uninit texture key with odd number of textures

src/gpu/gl/GrGLProgramDesc.cpp

Index: src/gpu/gl/GrGLProgramDesc.cpp
diff --git a/src/gpu/gl/GrGLProgramDesc.cpp b/src/gpu/gl/GrGLProgramDesc.cpp
index 032562550cec5d5541f5405f77fcb861e8b046ed..45e01e7c84c2b13a5170bce2e09edaa8e2e3482c 100644
--- a/src/gpu/gl/GrGLProgramDesc.cpp
+++ b/src/gpu/gl/GrGLProgramDesc.cpp
@@ -30,6 +30,10 @@ static void add_texture_key(GrProcessorKeyBuilder* b, const GrProcessor& proc,
         k16[i] = caps.configTextureSwizzle(access.getTexture()->config()).asKey() |
                  (isExternal ? 0xFF00 : 0x0000);
     }
+    // zero the last 16 bits if the number of textures is odd.
+    if (numTextures & 0x1) {
+        k16[numTextures] = 0;
+    }
 }
 
 /**