Fix CLPF test to avoid looking outside the frame

Change-Id: Iee9bc41a19d754e234a083f4416b938950f719a5

test/clpf_test.cc

@@ -109,7 +109,7 @@ void test_clpf(int w, int h, int depth, int iterations,
   // Test every combination of:
   // * Input with up to <depth> bits of noise
   // * Noise level around every value from 0 to (1<<depth)-1
-  // * Blocks anywhere in the frame (along all egdes and also fully inside)
+  // * Blocks anywhere in the frame (but not on the edge)
   // * All strengths
   // If clpf and ref_clpf are the same, we're just testing speed
   for (count = 0; count < iterations; count++) {
@@ -119,8 +119,8 @@ void test_clpf(int w, int h, int depth, int iterations,
           s[i] = clamp((rnd.Rand16() & ((1 << bits) - 1)) + level, 0,
                        (1 << depth) - 1);
 
-        for (ypos = 0; ypos < size && !error; ypos += h * !error) {
-          for (xpos = 0; xpos < size && !error; xpos += w * !error) {
+        for (ypos = 2; ypos < size - h - 2 && !error; ypos += h * !error) {
+          for (xpos = 2; xpos < size - w - 2 && !error; xpos += w * !error) {
             for (strength = depth - 8; strength < depth - 5 && !error;
                  strength += !error) {
               ref_clpf(s, ref_d, size, size, xpos, ypos, w, h, 1 << strength,