roachtest: ignore injected error in sqlsmith in some cases

We enable vectorized panic injection in `sqlsmith` roachtest, and we
generally don't expect it to be propagated all the way as "internal
error". However, sqlsmith itself issues some queries (like fetching all
DB regions) which might hit this injected error which will result in
a panic during `smither.Generate` call - we want to ignore such cases.

Release note: None

pkg/cmd/roachtest/tests/sqlsmith.go

@@ -271,11 +271,24 @@ WITH into_db = 'defaultdb', unsafe_restore_incompatible_version;
 						logStmt(stmt)
 						t.Fatalf("error: %s\nstmt:\n%s;", err, stmt)
 					}
-				} else if strings.Contains(es, "Empty statement returned by generate") ||
-					stmt == "" {
-					// Either were unable to generate a statement or
-					// we panicked making one.
-					t.Fatalf("Failed generating a query %s", err)
+				} else {
+					if strings.Contains(es, "Empty statement returned by generate") {
+						// We were unable to generate a statement - this is
+						// never expected.
+						t.Fatalf("Failed generating a query %s", err)
+					}
+					if stmt == "" {
+						// We panicked when generating a statement.
+						//
+						// The panic might be expected if it was a vectorized
+						// panic that was injected when sqlsmith itself issued a
+						// query to generate another query (for example, in
+						// getDatabaseRegions).
+						expectedError := strings.Contains(es, "injected panic in ")
+						if !expectedError {
+							t.Fatalf("Panicked when generating a query %s", err)
+						}
+					}
 				}
 				// Ignore other errors because they happen so
 				// frequently (due to sqlsmith not crafting