[inferbo] Fix an ignored case when the upper bounds of offset is +oo, and the upper bound of size is smaller than +oo

Summary:
The buffer overrun checker misses to handle the case when the upper bound of offset is +oo, and the upper bound of array size is less than +oo, which will causes false negative in some test cases.

For instance, for the following program,

```
int a[1];
for(int i=0; a[i]; i++) {}
```

The variable `i` will eventually be equal 1 and causes an overrun error within the loop statement. However, this error was missed by buffer overrun checker.

Author: sjxer723

infer/src/bufferoverrun/bufferOverrunProofObligations.ml

@@ -347,6 +347,10 @@ module ArrayAccessCondition = struct
       Bound.is_not_infty (ItvPure.ub real_idx) && Bound.le (ItvPure.ub size) (ItvPure.ub real_idx)
     then {report_issue_type= Issue IssueType.buffer_overrun_l2; propagate= false}
       (* symbolic il >= sl, probably an error *)
+    else if
+      Bound.is_infty (ItvPure.ub real_idx) && Bound.is_not_infty (ItvPure.ub size) 
+    then {report_issue_type= Issue IssueType.buffer_overrun_l3; propagate= false}
+      (* su < iu = +oo, probably an error *)
     else if
       Bound.is_symbolic (ItvPure.lb real_idx) && Bound.le (ItvPure.lb size) (ItvPure.lb real_idx)
     then {report_issue_type= Issue IssueType.buffer_overrun_s2; propagate= true}