Fix issue with branching to swapped stfld -> callvirt

Given the (abridged) psuedo-IL
```asm
ldfld PlayerData ...

ldfld bool   ...
brtrue.s     :opt

ldfld string ..
br.s         :set

opt:
ldfld string ...

set: stfld PlayerData::someField
```

We were patching it to the following:
```asm
ldfld PlayerData ...

ldfld bool   ...
brtrue.s     :opt

ldfld string ...
br.s         :set

opt:
ldfld string ...

ldstr "someField"
set: callvirt instance void PlayerData::SetStringSwappedArgs(string, string)
```

and the way we did this patching is by swapping an `stfld` to a `callvirt`
and then inserting the `ldstr` for the field name (which is the second arg
for our SetStringSwappedArgs) before this `callvirt` we inserted.
However, given this situation, we skip over the ldstr of the field name
when coming from the `false` branch path as it branches directly to
`set` as it had previously branched directly to an `stfld` and branching
is instruction location based.

The fix for this is relatively simple, just swap the `stfld` with the
`ldstr` instead, and then insert our `callvirt` afterwards, which gives
the following:

```asm
ldfld PlayerData ...

ldfld bool   ...
brtrue.s     :opt

ldfld string ...
br.s         :set

opt:
ldfld string ...

set: ldstr "someField"
callvirt instance void PlayerData::SetStringSwappedArgs(string, string)
```

PrePatcher/Program.cs

@@ -208,11 +208,11 @@ ILProcessor il
                 generic.GenericArguments.Add(field.FieldType);
                 callSet = Instruction.Create(OpCodes.Callvirt, generic);
             }
+
+            il.InsertAfter(instr, callSet);
 
-            instr.OpCode = callSet.OpCode;
-            instr.Operand = callSet.Operand;
-
-            il.InsertBefore(instr, ldstr);
+            instr.OpCode = ldstr.OpCode;
+            instr.Operand = ldstr.Operand;
         }
 
         private static void SwapLdFld
@@ -259,11 +259,11 @@ ILProcessor il
                 generic.GenericArguments.Add(field.FieldType);
                 callGet = Instruction.Create(OpCodes.Callvirt, generic);
             }
+
+            il.InsertAfter(instr, callGet);
 
-            instr.OpCode = callGet.OpCode;
-            instr.Operand = callGet.Operand;
-
-            il.InsertBefore(instr, ldstr);
+            instr.OpCode = ldstr.OpCode;
+            instr.Operand = ldstr.Operand;
         }
 
         private static MethodDefinition GenerateSwappedMethod(TypeDefinition methodParent, MethodReference oldMethod)