Allow PrevVendorApiLevel to be less than 34

Some developers need to set VendorApiLevel to 34. Though the
configuration is not officially supported, the ABI checker supports it
on a best-effort basis.

Test: make
Bug: 320347314
Change-Id: Ic3f5ea2028329f5d04606760b07947b7c98b2e51
diff --git a/android/config.go b/android/config.go
index f0854f9..9f009e4 100644
--- a/android/config.go
+++ b/android/config.go
@@ -1348,13 +1348,16 @@
 		panic(fmt.Errorf("Cannot parse vendor API level %s to an integer: %s",
 			c.VendorApiLevel(), err))
 	}
-	if vendorApiLevel < 202404 || vendorApiLevel%100 != 4 {
-		panic("Unknown vendor API level " + c.VendorApiLevel())
-	}
 	// The version before trunk stable is 34.
 	if vendorApiLevel == 202404 {
 		return "34"
 	}
+	if vendorApiLevel >= 1 && vendorApiLevel <= 34 {
+		return strconv.Itoa(vendorApiLevel - 1)
+	}
+	if vendorApiLevel < 202404 || vendorApiLevel%100 != 4 {
+		panic("Unknown vendor API level " + c.VendorApiLevel())
+	}
 	return strconv.Itoa(vendorApiLevel - 100)
 }