Fix #3264: Do not allow zero-length segments in CleanUpName: Escape p…

…ath separator characters at the start of a segment.

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs

@@ -692,7 +692,7 @@ static string CleanUpName(string text, bool separateAtDots, bool treatAsFileName
 					if (separateAtDots)
 						currentSegmentLength = 0;
 				}
-				else if (treatAsFileName && (c == '/' || c == '\\') && currentSegmentLength > 0)
+				else if (treatAsFileName && (c == '/' || c == '\\') && currentSegmentLength > 1)
 				{
 					// if we treat this as a file name, we've started a new segment
 					b.Append(c);