Fix potential division-by-zero

This was found by the fuzzer added in
#120

Signed-off-by: David Korczynski <david@adalogics.com>

include/hdr/hdr_histogram_log.h

@@ -20,6 +20,7 @@
 #define HDR_TRAILING_ZEROS_INVALID -29992
 #define HDR_VALUE_TRUNCATED -29991
 #define HDR_ENCODED_INPUT_TOO_LONG -29990
+#define HDR_INVALID_WORD_SIZE -29989
 
 #define HDR_LOG_TAG_MAX_BUFFER_LEN (1024)
 

src/hdr_histogram_log.c

@@ -101,6 +101,8 @@ const char* hdr_strerror(int errnum)
             return "Truncated value found when decoding";
         case HDR_ENCODED_INPUT_TOO_LONG:
             return "The encoded input exceeds the size of the histogram";
+        case HDR_INVALID_WORD_SIZE:
+            return "Invalid word size";
         default:
             return strerror(errnum);
     }
@@ -499,6 +501,10 @@ static int hdr_decode_compressed_v1(
     }
 
     word_size = word_size_from_cookie(be32toh(encoding_flyweight.cookie));
+    if (word_size == 0)
+    {
+        FAIL_AND_CLEANUP(cleanup, result, HDR_INVALID_WORD_SIZE);
+    }
     counts_limit = be32toh(encoding_flyweight.payload_len) / word_size;
     lowest_discernible_value = be64toh(encoding_flyweight.lowest_discernible_value);
     highest_trackable_value = be64toh(encoding_flyweight.highest_trackable_value);