Fix a crash on stroking empty paths with nv_path_rendering enabled

src/gpu/gl/GrGLPath.cpp

Index: src/gpu/gl/GrGLPath.cpp
diff --git a/src/gpu/gl/GrGLPath.cpp b/src/gpu/gl/GrGLPath.cpp
index 63c2fa107c66a0c3e2490636de81eda5fc9b3200..d46fa03b5e039e04248b4dfdc33466783edd0bce 100644
--- a/src/gpu/gl/GrGLPath.cpp
+++ b/src/gpu/gl/GrGLPath.cpp
@@ -59,13 +59,14 @@ inline int num_pts(const SkPath::Verb verb) {
 static const bool kIsWrapped = false; // The constructor creates the GL path object.
 
 GrGLPath::GrGLPath(GrGpuGL* gpu, const SkPath& path) : INHERITED(gpu, kIsWrapped) {
-    GL_CALL_RET(fPathID, GenPaths(1));
-    SkPath::Iter iter(path, true);
-
-    SkSTArray<16, GrGLubyte, true> pathCommands;
 #ifndef SK_SCALAR_IS_FLOAT
     GrCrash("Assumes scalar is float.");
 #endif
+    SkASSERT(!path.isEmpty());
+
+    GL_CALL_RET(fPathID, GenPaths(1));
+
+    SkSTArray<16, GrGLubyte, true> pathCommands;
     SkSTArray<16, SkPoint, true> pathPoints;
 
     int verbCnt = path.countVerbs();