mesa: fix more valgrind warnings

==27540== Invalid read of size 4
==27540==    at 0x96277B7: _mesa_make_extension_string (string3.h:144)
==27540==    by 0x9604E78: _mesa_make_current (context.c:1514)
==27540==    by 0x9602A8B: st_api_make_current (st_manager.c:789)
==27540==    by 0x45406E7: ???
==27540==  Address 0xad35b30 is 3,688 bytes inside a block of size 3,691 alloc'd
==27540==    at 0x4025315: calloc (vg_replace_malloc.c:467)
==27540==    by 0x9627641: _mesa_make_extension_string (extensions.c:910)
==27540==    by 0x9604E78: _mesa_make_current (context.c:1514)
==27540==    by 0x9602A8B: st_api_make_current (st_manager.c:789)
==27540==    by 0x45406E7: ???

And:

==28351== Invalid write of size 2
==28351==    at 0x4C087CC: _mesa_make_extension_string (string3.h:144)
==28351==    by 0x4BE6198: _mesa_make_current (context.c:1514)
==28351==    by 0x4BD4CAB: st_api_make_current (st_manager.c:789)
==28351==  Address 0x48dd1f3 is 19 bytes inside a block of size 20 alloc'd
==28351==    at 0x4025315: calloc (vg_replace_malloc.c:467)
==28351==    by 0x4C08711: _mesa_make_extension_string (extensions.c:778)
==28351==    by 0x4BE6198: _mesa_make_current (context.c:1514)
==28351==    by 0x4BD4CAB: st_api_make_current (st_manager.c:789)
==28351==
==28351== Invalid read of size 4
==28351==    at 0x4C087EC: _mesa_make_extension_string (extensions.c:806)
==28351==    by 0x4BE6198: _mesa_make_current (context.c:1514)
==28351==    by 0x4BD4CAB: st_api_make_current (st_manager.c:789)
==28351==  Address 0x48dd1f4 is 0 bytes after a block of size 20 alloc'd
==28351==    at 0x4025315: calloc (vg_replace_malloc.c:467)
==28351==    by 0x4C08711: _mesa_make_extension_string (extensions.c:778)
==28351==    by 0x4BE6198: _mesa_make_current (context.c:1514)
==28351==    by 0x4BD4CAB: st_api_make_current (st_manager.c:789)

The first part adds 2, because ' ' and '\0' may be written at the end
of the buffer.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/mesa/main/extensions.c b/src/mesa/main/extensions.c
index aceddaa3ef2..9cec15b5817 100644
--- a/src/mesa/main/extensions.c
+++ b/src/mesa/main/extensions.c
@@ -37,6 +37,8 @@
 #include "mfeatures.h"
 #include "mtypes.h"
 
+#define ALIGN(value, alignment)  (((value) + alignment - 1) & ~(alignment - 1))
+
 enum {
    DISABLE = 0,
    GL  = 1 << API_OPENGL,
@@ -773,7 +775,7 @@ get_extension_override( struct gl_context *ctx )
    }
 
    /* extra_exts: List of unrecognized extensions. */
-   extra_exts = calloc(strlen(env_const), sizeof(char));
+   extra_exts = calloc(ALIGN(strlen(env_const) + 2, 4), sizeof(char));
 
    /* Copy env_const because strtok() is destructive. */
    env = strdup(env_const);
@@ -907,7 +909,7 @@ _mesa_make_extension_string(struct gl_context *ctx)
    if (extra_extensions != NULL)
       length += 1 + strlen(extra_extensions); /* +1 for space */
 
-   exts = (char *) calloc(length + 1, sizeof(char));
+   exts = (char *) calloc(ALIGN(length + 1, 4), sizeof(char));
    if (exts == NULL) {
       free(extra_extensions);
       return NULL;