ProcRenderAddGlyphs: Avoid allocating a glyph just to find it cached

This is a cleanup without any real savings (yet). Previously, the
implementation would allocate a new glyph, then (often) find it in
the cache, and immediately discard the allocated object. This
re-organization first uses a new FindGlyphByHash function and only
allocates the glyph if nothing is found.

This isn't a real savings yet, since FindGlyphByHash currently still
does a temporary glyph allocation, but this is expected to be replaced
immediately as we switch to an alternate hashing mechanism (SHA1).

render/glyphstr.h

@@ -129,6 +129,12 @@ FindGlyphHashSet (CARD32 filled);
 GlyphRefPtr
 FindGlyphRef (GlyphHashPtr hash, CARD32 signature, Bool match, GlyphPtr compare);
 
+GlyphPtr
+FindGlyphByHash (CARD32	    hash,
+		 xGlyphInfo *gi,
+		 CARD8	    *bits,
+		 int	    format);
+
 CARD32
 HashGlyphInfoAndBits (xGlyphInfo *gi, CARD8 *data, unsigned int size);