Misc: Don't run etc1 bench with invalid image and fix VS2015 build warning

tools/sk_tool_utils.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "sk_tool_utils.h"
 #include "sk_tool_utils_flags.h"
 
@@ skipping 334 matching lines @@
     }
 }
 
 void make_big_path(SkPath& path) {
     #include "BigPathBench.inc"
 }
 
 static float gaussian2d_value(int x, int y, float sigma) {
     // don't bother with the scale term since we're just going to normalize the
     // kernel anyways
-    float temp = exp(-(x*x + y*y)/(2*sigma*sigma));
+    float temp = expf(-(x*x + y*y)/(2*sigma*sigma));
     return temp;
 }
 
 static float* create_2d_kernel(float sigma, int* filterSize) {
     // We will actually take 2*halfFilterSize+1 samples (i.e., our filter kernel
     // sizes are always odd)
     int halfFilterSize = SkScalarCeilToInt(6*sigma)/2;
     int wh = *filterSize = 2*halfFilterSize + 1;
 
     float* temp = new float[wh*wh];
@@ skipping 71 matching lines @@
     for (int y = 0; y < src.height(); ++y) {
         for (int x = 0; x < src.width(); ++x) {
             *dst.getAddr32(x, y) = blur_pixel(src, x, y, kernel.get(), wh);
         }
     }
  
     return dst;
 }
 
 }  // namespace sk_tool_utils