Fix crashes when vkAllocateMemory fails

[Upliner]

When system doesn't have enough VRAM, vkAllocateMemory fails and my app crashes. This patch fixes this by always checking return value of allocate_memory and allocate_dedicated_memory so my app can properly report error instead of crashing.

[codecov-commenter]

Codecov Report

:x: Patch coverage is 15.62500% with 27 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 95.87%. Comparing base (aad2e0c) to head (d5ab802). :warning: Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/allocator.cpp	15.62%	27 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5754      +/-   ##
==========================================
+ Coverage   95.84%   95.87%   +0.03%     
==========================================
  Files         837      837              
  Lines      264899   264931      +32     
==========================================
+ Hits       253889   254001     +112     
+ Misses      11010    10930      -80     

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[tencent-adm]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: Upliner
:x: nihui
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[github-actions[bot]]

The binary size change of libncnn.so (bytes)

architecture	base size	pr size	difference
x86_64	15155464	15155464	0 :kissing_heart:
armhf	6182208	6182336	+128 :warning:
aarch64	9520608	9454976	-65632 :kissing_heart: