fix(slots): fix conditional slot

fix #787

Author: yyx990803

packages/runtime-core/src/helpers/createSlots.ts

@@ -8,7 +8,10 @@ interface CompiledSlotDescriptor {
 
 export function createSlots(
   slots: Record<string, Slot>,
-  dynamicSlots: (CompiledSlotDescriptor | CompiledSlotDescriptor[])[]
+  dynamicSlots: (
+    | CompiledSlotDescriptor
+    | CompiledSlotDescriptor[]
+    | undefined)[]
 ): Record<string, Slot> {
   for (let i = 0; i < dynamicSlots.length; i++) {
     const slot = dynamicSlots[i]
@@ -17,7 +20,7 @@ export function createSlots(
       for (let j = 0; j < slot.length; j++) {
         slots[slot[j].name] = slot[j].fn
       }
-    } else {
+    } else if (slot) {
       // conditional single slot generated by <template v-if="..." #foo>
       slots[slot.name] = slot.fn
     }