Parameterized Vector4 is treated as Float3

A Parameterized Vector4 are being treated as Float3. This prevents users from being able to use Vector4s in an If node during runtime.

This is seen as far back as //UE4/Release4.22 cl 8065155 so this is not a regression.

1. Open any project
2. Create a new material
3. Open the material editor for that material
4. Creat an 'If' node
5. Create three Vector4 nodes
   • Hold '4' and Left mouse click on the graph
6. Create two Vector1 nodes
   • Hold '1' and Left mouse click on the graph
7. Connect the Vector nodes to the If Node inputs to match the attached screenshot
8. Connect the If node output to Base Color
9. Right click one of the Vector4 nodes and select Convert to Parameter

Result
The If node throws an error. "Arithmetic between types float3 and float4 are undefined"

Expected
No errors are thrown, material compiles successfully