mesa: fix issues causing warnings on Windows
diff --git a/src/mesa/shader/shader_api.c b/src/mesa/shader/shader_api.c
index 7c5a20b..161e8b6 100644
--- a/src/mesa/shader/shader_api.c
+++ b/src/mesa/shader/shader_api.c
@@ -512,7 +512,7 @@
 {
    struct gl_shader_program *shProg;
    const GLint size = -1; /* unknown size */
-   GLint i;
+   GLint i, oldIndex;
    GLenum datatype = GL_FLOAT_VEC4;
 
    shProg = _mesa_lookup_shader_program_err(ctx, program,
@@ -535,6 +535,14 @@
       return;
    }
 
+   if (shProg->LinkStatus) {
+      /* get current index/location for the attribute */
+      oldIndex = _mesa_get_attrib_location(ctx, program, name);
+   }
+   else {
+      oldIndex = -1;
+   }
+
    /* this will replace the current value if it's already in the list */
    i = _mesa_add_attribute(shProg->Attributes, name, size, datatype, index);
    if (i < 0) {