mesa: Fix remove_instructions to successfully remove when removeFlags[0].

This fixes the dead code elimination to work on the particular code
mentioned in the previous commit.

src/mesa/shader/prog_optimize.c

@@ -73,6 +73,12 @@ remove_instructions(struct gl_program *prog, const GLboolean *removeFlags)
          }
       }
    }
+   /* Finish removing if the first instruction was to be removed. */
+   if (removeCount > 0) {
+      GLint removeStart = removeEnd - removeCount + 1;
+      _mesa_delete_instructions(prog, removeStart, removeCount);
+      removeStart = removeCount = 0; /* reset removal info */
+   }
    return totalRemoved;
 }