Fix issues in botan shown up by a coverity scan

Reviewed-by: kh

src/libs/3rdparty/botan/src/alloc/mem_pool/mem_pool.cpp

@@ -180,7 +180,7 @@ void Pooling_Allocator::deallocate(void* ptr, u32bit n)
    const u32bit BITMAP_SIZE = Memory_Block::bitmap_size();
    const u32bit BLOCK_SIZE = Memory_Block::block_size();
 
-   if(ptr == 0 && n == 0)
+   if(ptr == 0 || n == 0)
       return;
 
    Mutex_Holder lock(mutex);

src/libs/3rdparty/botan/src/pk_pad/emsa2/emsa2.cpp

@@ -103,8 +103,9 @@ EMSA2::EMSA2(HashFunction* hash_in) : hash(hash_in)
 
    if(hash_id == 0)
       {
+      std::string hashname = hash->name();
       delete hash;
-      throw Encoding_Error("EMSA2 cannot be used with " + hash->name());
+      throw Encoding_Error("EMSA2 cannot be used with " + hashname);
       }
    }
 

src/libs/3rdparty/botan/src/rng/randpool/randpool.cpp

@@ -186,10 +186,11 @@ Randpool::Randpool(BlockCipher* cipher_in,
       !cipher->valid_keylength(OUTPUT_LENGTH) ||
       !mac->valid_keylength(OUTPUT_LENGTH))
       {
+      std::string ciphername = cipher->name(), macname = mac->name();
       delete cipher;
       delete mac;
       throw Internal_Error("Randpool: Invalid algorithm combination " +
-                           cipher->name() + "/" + mac->name());
+                           ciphername + "/" + macname);
       }
 
    buffer.create(BLOCK_SIZE);