Fix GH-9971: Incorrect NUMERIC value returned from PDO_Firebird

Dialect 1 databases store and transfer `NUMERIC(15,2)` values as
doubles, which we need to cater to in `firebird_stmt_get_col()` to
avoid `ZEND_ASSUME(0)` to ever be triggered, since that may result
in undefined behavior.

Since adding a regression test would require to create a dialect 1
database, we go without it.

Closes GH-10021.

Author: cmb69

NEWS

@@ -36,6 +36,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-9298 (Signal handler called after rshutdown leads to crash).
     (Erki Aring)
 
+- PDO_Firebird:
+  . Fixed bug GH-9971 (Incorrect NUMERIC value returned from PDO_Firebird).
+    (cmb)
+
 - Session:
   . Fixed GH-9932 (session name silently fails with . and [). (David Carlier)
 

ext/pdo_firebird/firebird_statement.c

@@ -382,6 +382,8 @@ static int firebird_stmt_get_col(
 				case SQL_INT64:
 					n = *(ISC_INT64*)var->sqldata;
 					break;
+				case SQL_DOUBLE:
+					break;
 				EMPTY_SWITCH_DEFAULT_CASE()
 			}