Fix (unreported) Separate bones creates empty armature

Fix for fix (rB8bf7ca9fe31c).
The fix was not actually working [neither for multi-armature-editing as
intended nor for single armatures] and it broke single-armature bone
separation completely.

More or less indentation issue, move relevant code out of bone loop, do
after all bones have been checked, guess this was intended anyways.

Differential Revision: https://developer.blender.org/D6949

source/blender/editors/armature/armature_relations.c

@@ -639,14 +639,14 @@ static int separate_armature_exec(bContext *C, wmOperator *op)
             has_selected_any = true;
           }
         }
-        if (has_selected_bone == false) {
-          if (has_selected_any) {
-            /* Without this, we may leave head/tail selected
-             * which isn't expected after separating. */
-            ED_armature_edit_deselect_all(ob_old);
-          }
-          continue;
+      }
+      if (has_selected_bone == false) {
+        if (has_selected_any) {
+          /* Without this, we may leave head/tail selected
+           * which isn't expected after separating. */
+          ED_armature_edit_deselect_all(ob_old);
         }
+        continue;
       }
     }