Remove useless checks for NULL before freeing

This patch has been generated by the following Coccinelle semantic
patch:

// Remove useless checks for NULL before freeing
//
// free (NULL) is a no-op, so there is no need to avoid it

@@
expression E;
@@
+ free (E);
+ E = NULL;
- if (unlikely (E != NULL)) {
-   free(E);
(
-   E = NULL;
|
-   E = 0;
)
   ...
- }

@@
expression E;
type T;
@@
+ free ((T) E);
+ E = NULL;
- if (unlikely (E != NULL)) {
-   free((T) E);
(
-   E = NULL;
|
-   E = 0;
)
   ...
- }

@@
expression E;
@@
+ free (E);
- if (unlikely (E != NULL)) {
-   free (E);
- }

@@
expression E;
type T;
@@
+ free ((T) E);
- if (unlikely (E != NULL)) {
-   free ((T) E);
- }

Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/main/shaderapi.c

@@ -703,9 +703,7 @@ shader_source(struct gl_context *ctx, GLuint shader, const GLchar *source)
       return;
 
    /* free old shader source string and install new one */
-   if (sh->Source) {
-      free((void *) sh->Source);
-   }
+   free((void *)sh->Source);
    sh->Source = source;
    sh->CompileStatus = GL_FALSE;
 #ifdef DEBUG