fix:select from table not exist cause panic

[gongna-au]

What this PR does:

Which issue(s) this PR fixes:

Fixes #660

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.12 ⚠️

Comparison is base (c696476) 36.42% compared to head (cd5c332) 36.30%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #693      +/-   ##
==========================================
- Coverage   36.42%   36.30%   -0.12%     
==========================================
  Files         228      228              
  Lines       23759    23850      +91     
==========================================
+ Hits         8654     8659       +5     
- Misses      14106    14192      +86     
  Partials      999      999              

Impacted Files	Coverage Δ
pkg/constants/mysql/constants.go	100.00% <ø> (ø)
pkg/runtime/optimize/dml/select.go	0.75% <0.00%> (+0.30%)	⬆️

... and 1 file with indirect coverage changes

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