mruby-compiler: fix sp imbalance in pattern matching with rescue

The => pattern matching codegen was doing push() after RAISEIF, even though
RAISEIF never returns. This caused sp to be off by 1 when success and failure
paths joined, resulting in wrong register allocation for subsequent operations.

For string interpolation like "#{ expr => pattern rescue body }", the base
string would be at R2 but STRCAT would incorrectly use R3, causing memory
corruption and crashes.

Test case: %{#{.=>.,. rescue def .()end}} (from oss-fuzz)

Co-authored-by: Claude <noreply@anthropic.com>

mrbgems/mruby-compiler/core/codegen.c

@@ -6655,7 +6655,7 @@ codegen(codegen_scope *s, node *tree, int val)
           genop_3(s, OP_SEND, exc_reg, sym_idx(s, MRB_SYM_2(s->mrb, new)), 1);
           /* Raise the exception */
           genop_1(s, OP_RAISEIF, exc_reg);
-          if (val) push();
+          /* No push here: RAISEIF never returns, control transfers to rescue handler */
         }
         else {
           /* expr in pattern: return false */