free -> WebPSafeFree()

avoids unbalanced memory track at the end (w/ PRINT_MEM_INFO flag on)

Change-Id: I70da087f079198bcaacd0c81593f104058dcac69

src/enc/vp8l.c

@@ -290,7 +290,7 @@ static int AnalyzeEntropy(const uint32_t* argb,
         }
       }
     }
-    free(histo);
+    WebPSafeFree(histo);
     return 1;
   } else {
     return 0;