Fix NULL handling in FQexecParams()

It turns out that if a column has a NOT NULL constraint, but
the provided parameter for that column is NULL, if var->sqldata is
allocated, the column will be filled with whatever the allocated
memory contains (probably garbage, as we weren't initialising it).

This does not happen if the column has no NOT NULL constraint.

Author: ibarwick

CHANGELOG

@@ -1,5 +1,8 @@
 Revision history for libfq
 
+0.4.3	2022-02-??
+	- Fix NULL value handling in FQexecParams()
+
 0.4.2	2020-10-17
 	- Add configure option "--with-fbclient"
 	- Fix FQexplainStatement() output

src/libfq.c

@@ -1541,11 +1541,9 @@ _FQexecParams(FBconn *conn,
 					_FQexecClearResult(result);
 			}
 
+			/* var->sqldata remains NULL to indicate NULL */
 			if (size >= 0)
-			{
-				var->sqldata = (char *)malloc(size);
 				var->sqllen = size;
-			}
 		}
 		else
 		{