fix LoadSHRTransition and document the underlying cause

src/glue.prorwts2.a

@@ -49,6 +49,10 @@ gRootDirectory
 ;        +1 address of filename
 ; out:   all flags clobbered
 ;        all registers clobbered
+;        filename clobbered (hey, this is important, you can't call this with
+;          the same filename buffer twice unless you REALLY know what you're
+;          doing, so you should probably use one of the LOAD_* macros which
+;          copies the filename to a temporary buffer)
 ;        stack set to next instruction after parameters
 ;------------------------------------------------------------------------------
 LoadFile

src/ui.attract.shr.a

@@ -31,12 +31,14 @@ SHRArtworkSlideshow
 ;        $A000..$BFFF/main contains transition effect code
 ;------------------------------------------------------------------------------
 LoadSHRTransition
-         jsr   LoadFile
+         +LDADDR kSFXFizzleFile
-         !word kSFXFizzleFile
+         +STAY @file
+         +LOAD_FILE kFXDirectory, @file
          rts
+@file    !word $FDFD
 kSFXFizzleFile
          !byte @kSFXFizzleFile_e-*-1
-         !text "FX/SHR.FIZZLE"
+         !text "SHR.FIZZLE"
 @kSFXFizzleFile_e
 
 ;------------------------------------------------------------------------------