Rearrange logic for incrementals

* Require incremental arg and parse it once outside loop.

lineage-updater

@@ -165,6 +165,11 @@ def find_roms(device=None, buildtype=None, incremental=None):
         cf.close()
         cf = None
 
+    try:
+        req_incr_stamp = incremental_stamp(incremental)
+    except Exception as e:
+        raise RuntimeError("Failed to parse request incremental field: %s" % (e))
+
     roms = []
     for k, v in cache.items():
         try:
@@ -177,22 +182,18 @@ def find_roms(device=None, buildtype=None, incremental=None):
             continue
         if buildtype and props['buildtype'] != buildtype:
             continue
-        if incremental:
-            if 'incrbase' in props:
-                # Incremental
-                if incremental != props['incrbase']:
-                    continue
-            else:
-                # Full
-                try:
-                    req_incr_stamp = incremental_stamp(incremental)
-                except ValueError:
-                    continue
+
         try:
             ota_incr_stamp = incremental_stamp(props['incremental'])
         except ValueError:
             dbg("Failed to parse cache incremental field")
             continue
+
+        if 'incrbase' in props:
+            # Incremental
+            if incremental != props['incrbase']:
+                continue
+
         if ota_incr_stamp <= req_incr_stamp:
             continue