Avoid creation of unnecessary image bufs (at alt-text to img switch)

This is the first of a patch series for image code bugs that have
severe impact on performance.

With these testing files:

1imgA.html  =  <img src="maj00s.png" alt="img1">
2imgSA.html  = <img src="maj00s.png" alt="img1">
               <img src="maj00s.png" alt="img12">
3imgSA.html  = <img src="maj00s.png" alt="img1">
               <img src="maj00s.png" alt="img12">
               <img src="maj00s.png" alt="img123">

2imgA.html  =  <img src="maj00s.png" alt="img1">
               <img src="maj21s.png" alt="img12">
3imgA.html  =  <img src="maj00s.png" alt="img1">
               <img src="maj21s.png" alt="img12">
               <img src="c10s.png" alt="img123">

This are the results:

.------------------------------------------------------------------.
|imgbufs     |         No patch         |         Patched #1       |
|            | first time | upon reload | first time | upon reload |
|-------------------------------------------------------------------
|1imgA.html  |     2      |     1       |     1      |      1      |
|2imgSA.html |     3      |     2       |     1      |      2      |
|3imgSA.html |     4      |     3       |     1      |      3      |
|-------------------------------------------------------------------
|2imgA.html  |     4      |     2       |     2      |      2      |
|3imgA.html  |     6      |     3       |     3      |      3      |
'------------------------------------------------------------------'

1 files changed, 4 insertions, 2 deletions

diff --git a/src/dicache.c b/src/dicache.c
index db3b86b2..b63e9d3b 100644
--- a/src/dicache.c
+++ b/src/dicache.c
@@ -256,7 +256,9 @@ void a_Dicache_invalidate_entry(const DilloUrl *Url)
 
 /*
  * Set image's width, height & type
- * (By now, we'll use the image information despite the html tags --Jcid)
+ * - 'width' and 'height' come from the image data.
+ * - HTML width and height attrs are handled with setNonCssHint.
+ * - CSS sizing is handled by the CSS engine.
  */
 void a_Dicache_set_parms(DilloUrl *url, int version, DilloImage *Image,
                          uint_t width, uint_t height, DilloImgType type,
@@ -269,7 +271,7 @@ void a_Dicache_set_parms(DilloUrl *url, int version, DilloImage *Image,
    /* Find the DicEntry for this Image */
    DicEntry = a_Dicache_get_entry(url, version);
    dReturn_if_fail ( DicEntry != NULL );
-   /* Parameters already set? */
+   /* Parameters already set? Don't do it twice. */
    dReturn_if_fail ( DicEntry->State < DIC_SetParms );
 
    _MSG("  RefCount=%d version=%d\n", DicEntry->RefCount, DicEntry->version);