Fixed buffer size for empty sparsevec with max dimensions (no impact to users due to Postgres allocation alignment) [skip ci]

Co-authored-by: 0xJi3F
(cherry picked from commit 5ffa6d022b211c89bb69bfd1d91cafbfeac8345a)

src/sparsevec.c

@@ -434,13 +434,13 @@ sparsevec_out(PG_FUNCTION_ARGS)
 	 * nnz * (FLOAT_SHORTEST_DECIMAL_LEN - 1) bytes for
 	 * float_to_shortest_decimal_bufn
 	 *
-	 * nnz - 1 bytes for ,
+	 * max(nnz - 1, 0) bytes for ,
 	 *
 	 * 10 bytes for dimensions
 	 *
 	 * 4 bytes for {, }, /, and \0
 	 */
-	buf = (char *) palloc((11 + FLOAT_SHORTEST_DECIMAL_LEN) * sparsevec->nnz + 13);
+	buf = (char *) palloc((11 + FLOAT_SHORTEST_DECIMAL_LEN) * sparsevec->nnz + 14);
 	ptr = buf;
 
 	AppendChar(ptr, '{');

test/expected/sparsevec.out

@@ -187,6 +187,12 @@ SELECT '{}/-1'::sparsevec;
 ERROR:  sparsevec must have at least 1 dimension
 LINE 1: SELECT '{}/-1'::sparsevec;
                ^
+SELECT '{}/1000000000'::sparsevec;
+   sparsevec   
+---------------
+ {}/1000000000
+(1 row)
+
 SELECT '{}/1000000001'::sparsevec;
 ERROR:  sparsevec cannot have more than 1000000000 dimensions
 LINE 1: SELECT '{}/1000000001'::sparsevec;

test/sql/sparsevec.sql

@@ -38,6 +38,7 @@ SELECT '{1:1,1:1}/2'::sparsevec;
 SELECT '{1:1,2:1,1:1}/2'::sparsevec;
 SELECT '{}/5'::sparsevec;
 SELECT '{}/-1'::sparsevec;
+SELECT '{}/1000000000'::sparsevec;
 SELECT '{}/1000000001'::sparsevec;
 SELECT '{}/2147483648'::sparsevec;
 SELECT '{}/-2147483649'::sparsevec;