fix(json): signed integer overflow if value is UA_INT64_MIN

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=15334
Credit to oss-fuzz

deps/itoa.c

@@ -69,12 +69,23 @@ UA_UInt16 itoaUnsigned(UA_UInt64 value, char* buffer, UA_Byte base) {
 /* adapted from http://www.techiedelight.com/implement-itoa-function-in-c/ to use UA_... types */
 UA_UInt16 itoaSigned(UA_Int64 value, char* buffer) {
     /* consider absolute value of number */
-    UA_UInt64 n = (UA_UInt64)value;
 
-    if(value < 0){
-        n = (UA_UInt64)-value;
+
+    UA_UInt64 n;
+
+    /* Special case for UA_INT64_MIN which can not simply be negated */
+    /* it will cause a signed integer overflow */
+    if (value == UA_INT64_MIN) {
+        n = (UA_UInt64)UA_INT64_MAX + 1;
     }
-    
+    else {
+        n = (UA_UInt64)value;
+
+        if(value < 0){
+            n = (UA_UInt64)-value;
+        }
+    }
+
     UA_UInt16 i = 0;
     while (n) {
         UA_UInt64 r = n % 10;

include/open62541/types.h

@@ -104,8 +104,8 @@ typedef uint32_t UA_UInt32;
  * An integer value between -9 223 372 036 854 775 808 and
  * 9 223 372 036 854 775 807. */
 typedef int64_t UA_Int64;
-#define UA_INT64_MIN ((int64_t)-9223372036854775808)
-#define UA_INT64_MAX (int64_t)9223372036854775807
+#define UA_INT64_MAX (int64_t)9223372036854775807LL
+#define UA_INT64_MIN ((int64_t)-UA_INT64_MAX-1LL)
 
 /**
  * UInt64
@@ -113,7 +113,7 @@ typedef int64_t UA_Int64;
  * An integer value between 0 and 18 446 744 073 709 551 615. */
 typedef uint64_t UA_UInt64;
 #define UA_UINT64_MIN (uint64_t)0
-#define UA_UINT64_MAX (uint64_t)18446744073709551615
+#define UA_UINT64_MAX (uint64_t)18446744073709551615ULL
 
 /**
  * Float