libmach: fix crash in dwarfpc (misuse of realloc)

R=rsc
CC=plan9port.codebot
https://codereview.appspot.com/7225059
diff --git a/src/libmach/dwarfpc.c b/src/libmach/dwarfpc.c
index 9c36cf0..31b6bb4 100644
--- a/src/libmach/dwarfpc.c
+++ b/src/libmach/dwarfpc.c
@@ -194,6 +194,7 @@
 					newf = realloc(f, (nf+1)*sizeof(f[0]));
 					if(newf == nil)
 						goto out;
+					f = newf;
 					f[nf++] = b.p;
 					s = dwarfgetstring(&b);
 					dwarfget128(&b);