Fill SkRRect::fType proactively.

I found no external mentions of SkRRect::kUnknown_Type.

Motivating race found by TSAN:
http://build.chromium.org/p/client.skia/builders/Test-Ubuntu13.10-GCE-NoGPU-x86_64-Release-TSAN-Trybot/builds/48/steps/dm/logs/stdio

BUG=skia:

Review URL: https://codereview.chromium.org/801693003
diff --git a/src/utils/SkLua.cpp b/src/utils/SkLua.cpp
index baddb1a..2370b99 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -187,7 +187,7 @@
 static SkScalar getarray_scalar(lua_State* L, int stackIndex, int arrayIndex) {
     SkASSERT(lua_istable(L, stackIndex));
     lua_rawgeti(L, stackIndex, arrayIndex);
-    
+
     SkScalar value = lua2scalar(L, -1);
     lua_pop(L, 1);
     return value;
@@ -404,7 +404,7 @@
     SkASSERT(lua_istable(L, index));
     lua_pushstring(L, key);
     lua_gettable(L, index);
-    
+
     SkScalar value = lua2scalar(L, -1);
     lua_pop(L, 1);
     return value;
@@ -533,7 +533,7 @@
         srcRPtr = lua2rect(L, 3, &srcR);
     }
     lua2rect(L, 4, &dstR);
-    
+
     SkPaint paint;
     canvas->drawImageRect(image, srcRPtr, dstR, lua2OptionalPaint(L, 5, &paint));
     return 0;
@@ -1579,7 +1579,6 @@
 
 static const char* rrect_type(const SkRRect& rr) {
     switch (rr.getType()) {
-        case SkRRect::kUnknown_Type: return "unknown";
         case SkRRect::kEmpty_Type: return "empty";
         case SkRRect::kRect_Type: return "rect";
         case SkRRect::kOval_Type: return "oval";