Fix pg_dump's --if-exists for large objects

This was born broken in 9067310c.

Per trouble report from Joachim Wieland.

Pavel Stěhule and Álvaro Herrera

src/bin/pg_dump/pg_backup_archiver.c

@@ -439,6 +439,20 @@ RestoreArchive(Archive *AHX)
 						ahprintf(AH, "%s", te->dropStmt);
 					}
 					else
+					{
+						/*
+						 * Inject an appropriate spelling of "if exists".  For
+						 * large objects, we have a separate routine that
+						 * knows how to do it, without depending on
+						 * te->dropStmt; use that.  For other objects we need
+						 * to parse the command.
+						 *
+						 */
+						if (strncmp(te->desc, "BLOB", 4) == 0)
+						{
+							DropBlobIfExists(AH, te->catalogId.oid);
+						}
+						else
 						{
 							char		buffer[40];
 							char	   *mark;
@@ -447,8 +461,8 @@ RestoreArchive(Archive *AHX)
 							PQExpBuffer ftStmt = createPQExpBuffer();
 
 							/*
-						 * Need to inject IF EXISTS clause after ALTER TABLE
-						 * part in ALTER TABLE .. DROP statement
+							 * Need to inject IF EXISTS clause after ALTER
+							 * TABLE part in ALTER TABLE .. DROP statement
 							 */
 							if (strncmp(dropStmt, "ALTER TABLE", 11) == 0)
 							{
@@ -458,15 +472,15 @@ RestoreArchive(Archive *AHX)
 							}
 
 							/*
-						 * ALTER TABLE..ALTER COLUMN..DROP DEFAULT does not
-						 * support the IF EXISTS clause, and therefore we
-						 * simply emit the original command for such objects.
-						 * For other objects, we need to extract the first
-						 * part of the DROP which includes the object type.
-						 * Most of the time this matches te->desc, so search
-						 * for that; however for the different kinds of
-						 * CONSTRAINTs, we know to search for hardcoded "DROP
-						 * CONSTRAINT" instead.
+							 * ALTER TABLE..ALTER COLUMN..DROP DEFAULT does
+							 * not support the IF EXISTS clause, and therefore
+							 * we simply emit the original command for such
+							 * objects. For other objects, we need to extract
+							 * the first part of the DROP which includes the
+							 * object type. Most of the time this matches
+							 * te->desc, so search for that; however for the
+							 * different kinds of CONSTRAINTs, we know to
+							 * search for hardcoded "DROP CONSTRAINT" instead.
 							 */
 							if (strcmp(te->desc, "DEFAULT") == 0)
 								appendPQExpBuffer(ftStmt, "%s", dropStmt);
@@ -498,6 +512,7 @@ RestoreArchive(Archive *AHX)
 					}
 				}
 			}
+		}
 
 		/*
 		 * _selectOutputSchema may have set currSchema to reflect the effect