pg_dump: Fix crash with invalid pg_cast row

An invalid combination of pg_cast.castfunc and pg_cast.castmethod
would result in a segmentation fault.  Now it prints a warning.

found by Coverity

src/bin/pg_dump/pg_dump.c

@@ -9477,6 +9477,7 @@ dumpCast(Archive *fout, CastInfo *cast)
 			appendPQExpBuffer(defqry, "WITH INOUT");
 			break;
 		case COERCION_METHOD_FUNCTION:
+			if (funcInfo)
 			{
 				char   *fsig = format_function_signature(fout, funcInfo, true);
 
@@ -9487,8 +9488,10 @@ dumpCast(Archive *fout, CastInfo *cast)
 				appendPQExpBuffer(defqry, "WITH FUNCTION %s.%s",
 								  fmtId(funcInfo->dobj.namespace->dobj.name), fsig);
 				free(fsig);
-			break;
 			}
+			else
+				write_msg(NULL, "WARNING: bogus value in pg_cast.castfunc or pg_cast.castmethod field\n");
+			break;
 		default:
 			write_msg(NULL, "WARNING: bogus value in pg_cast.castmethod field\n");
 	}