RAM Search: Fix unhandled exception

Fixes an unhandled exception when beginning to type a negative number
into the search box when display is set to float

BizHawk.Client.EmuHawk/tools/Watch/WatchValueBox.cs

@@ -686,6 +686,8 @@ namespace BizHawk.Client.EmuHawk
 				case DisplayType.Float:
 					if (Text.IsFloat())
 					{
+						if (Text == "-")
+							return 0;
 						float val = float.Parse(Text);
 						var bytes = BitConverter.GetBytes(val);
 						return BitConverter.ToInt32(bytes, 0);