Fix some jsonb issues found by Coverity in recent commits.

Mostly these issues concern the non-use of function results. These
have been changed to use (void) pushJsonbValue(...) instead of assigning
the result to a variable that gets overwritten before it is used.

There is a larger issue that we should possibly examine the API for
pushJsonbValue(), so that instead of returning a value it modifies a
state argument. The current idiom is rather clumsy. However, changing
that requires quite a bit more work, so this change should do for the
moment.

src/backend/utils/adt/jsonb.c

@@ -1194,7 +1194,7 @@ jsonb_build_object_noargs(PG_FUNCTION_ARGS)
 
 	memset(&result, 0, sizeof(JsonbInState));
 
-	result.res = pushJsonbValue(&result.parseState, WJB_BEGIN_OBJECT, NULL);
+	(void) pushJsonbValue(&result.parseState, WJB_BEGIN_OBJECT, NULL);
 	result.res = pushJsonbValue(&result.parseState, WJB_END_OBJECT, NULL);
 
 	PG_RETURN_POINTER(JsonbValueToJsonb(result.res));
@@ -1255,7 +1255,7 @@ jsonb_build_array_noargs(PG_FUNCTION_ARGS)
 
 	memset(&result, 0, sizeof(JsonbInState));
 
-	result.res = pushJsonbValue(&result.parseState, WJB_BEGIN_ARRAY, NULL);
+	(void) pushJsonbValue(&result.parseState, WJB_BEGIN_ARRAY, NULL);
 	result.res = pushJsonbValue(&result.parseState, WJB_END_ARRAY, NULL);
 
 	PG_RETURN_POINTER(JsonbValueToJsonb(result.res));
@@ -1283,7 +1283,7 @@ jsonb_object(PG_FUNCTION_ARGS)
 
 	memset(&result, 0, sizeof(JsonbInState));
 
-	result.res = pushJsonbValue(&result.parseState, WJB_BEGIN_OBJECT, NULL);
+	(void) pushJsonbValue(&result.parseState, WJB_BEGIN_OBJECT, NULL);
 
 	switch (ndims)
 	{
@@ -1336,7 +1336,7 @@ jsonb_object(PG_FUNCTION_ARGS)
 		v.val.string.len = len;
 		v.val.string.val = str;
 
-		result.res = pushJsonbValue(&result.parseState, WJB_KEY, &v);
+		(void) pushJsonbValue(&result.parseState, WJB_KEY, &v);
 
 		if (in_nulls[i * 2 + 1])
 		{
@@ -1353,7 +1353,7 @@ jsonb_object(PG_FUNCTION_ARGS)
 			v.val.string.val = str;
 		}
 
-		result.res = pushJsonbValue(&result.parseState, WJB_VALUE, &v);
+		(void) pushJsonbValue(&result.parseState, WJB_VALUE, &v);
 	}
 
 	pfree(in_datums);
@@ -1389,7 +1389,7 @@ jsonb_object_two_arg(PG_FUNCTION_ARGS)
 
 	memset(&result, 0, sizeof(JsonbInState));
 
-	result.res = pushJsonbValue(&result.parseState, WJB_BEGIN_OBJECT, NULL);
+	(void) pushJsonbValue(&result.parseState, WJB_BEGIN_OBJECT, NULL);
 
 	if (nkdims > 1 || nkdims != nvdims)
 		ereport(ERROR,
@@ -1431,7 +1431,7 @@ jsonb_object_two_arg(PG_FUNCTION_ARGS)
 		v.val.string.len = len;
 		v.val.string.val = str;
 
-		result.res = pushJsonbValue(&result.parseState, WJB_KEY, &v);
+		(void) pushJsonbValue(&result.parseState, WJB_KEY, &v);
 
 		if (val_nulls[i])
 		{
@@ -1448,7 +1448,7 @@ jsonb_object_two_arg(PG_FUNCTION_ARGS)
 			v.val.string.val = str;
 		}
 
-		result.res = pushJsonbValue(&result.parseState, WJB_VALUE, &v);
+		(void) pushJsonbValue(&result.parseState, WJB_VALUE, &v);
 	}
 
 	result.res = pushJsonbValue(&result.parseState, WJB_END_OBJECT, NULL);

src/backend/utils/adt/jsonfuncs.c

@@ -3182,7 +3182,7 @@ jsonb_strip_nulls(PG_FUNCTION_ARGS)
 				continue;
 
 			/* otherwise, do a delayed push of the key */
-			res = pushJsonbValue(&parseState, WJB_KEY, &k);
+			(void) pushJsonbValue(&parseState, WJB_KEY, &k);
 		}
 
 		if (type == WJB_VALUE || type == WJB_ELEM)
@@ -3191,5 +3191,7 @@ jsonb_strip_nulls(PG_FUNCTION_ARGS)
 			res = pushJsonbValue(&parseState, type, NULL);
 	}
 
+	Assert(res != NULL);
+
 	PG_RETURN_POINTER(JsonbValueToJsonb(res));
 }