Common/FileSystem: Fix canonicalization of paths beginning with `./`

If we don't skip past the following separator when the destination
is empty, then `./file` gets canonicalized as `/file`.

Also, consider the case where we end up with an empty string (for
example, from `foo/..`). Canonicalize this as `.`.

src/common/file_system.cpp

@@ -75,6 +75,9 @@ void CanonicalizePath(char* Destination, u32 cbDestination, const char* Path, bo
           // remove the previous \, if we have one trailing the dot it'll append it anyway
           if (destinationLength > 0)
             Destination[--destinationLength] = '\0';
+          // if there was no previous \, skip past the next one
+          else if (nextCh != '\0')
+            i++;
 
           continue;
         }
@@ -126,6 +129,10 @@ void CanonicalizePath(char* Destination, u32 cbDestination, const char* Path, bo
     i++;
   }
 
+  // if we end up with the empty string, return '.'
+  if (destinationLength == 0)
+    Destination[destinationLength++] = '.';
+
   // ensure nullptr termination
   if (destinationLength < cbDestination)
     Destination[destinationLength] = '\0';