Eevee: Fix crash with volumetrics + default mat + alpha blend

source/blender/draw/engines/eevee/eevee_private.h

@@ -107,18 +107,18 @@ enum {
 	VAR_MAT_BLEND    = (1 << 4),
 	VAR_MAT_VSM      = (1 << 5),
 	VAR_MAT_ESM      = (1 << 6),
+	VAR_MAT_VOLUME   = (1 << 7),
 	/* Max number of variation */
 	/* IMPORTANT : Leave it last and set
 	 * it's value accordingly. */
-	VAR_MAT_MAX      = (1 << 7),
+	VAR_MAT_MAX      = (1 << 8),
 	/* These are options that are not counted in VAR_MAT_MAX
 	 * because they are not cumulative with the others above. */
-	VAR_MAT_CLIP     = (1 << 8),
-	VAR_MAT_HASH     = (1 << 9),
-	VAR_MAT_MULT     = (1 << 10),
-	VAR_MAT_SHADOW   = (1 << 11),
-	VAR_MAT_REFRACT  = (1 << 12),
-	VAR_MAT_VOLUME   = (1 << 13),
+	VAR_MAT_CLIP     = (1 << 9),
+	VAR_MAT_HASH     = (1 << 10),
+	VAR_MAT_MULT     = (1 << 11),
+	VAR_MAT_SHADOW   = (1 << 12),
+	VAR_MAT_REFRACT  = (1 << 13),
 	VAR_MAT_SSS      = (1 << 14),
 	VAR_MAT_TRANSLUC = (1 << 15),
 	VAR_MAT_SSSALBED = (1 << 16),